This is a really interesting question.

I buy two types of faces: workhorse fonts that I know I will use a lot, and specific one-purpose fonts for a specific project. In theory, I don't anticipate using the latter group ever again after the project is complete, although of course I always do.

I, too, am also very frugal. I rarely buy fonts at all. I have, in fact, very few good ones. Typefaces are very expensive, especially for a freelancer, as they have to come out of my profit. So I have to choose very carefully.

With general-purpose serifed text faces, I want, when possible, to purchase the whole family: Roman and italic in all optical sizes. (I almost never need bold or any weight other than regular, and I never need condensed or expanded versions. But if you're going to buy that much of the family, it's usually cost effective to get the whole thing. And sometimes the weights come in handy.) So every couple of years I will buy a new text family. And then I will basically use it all the time for a few years, until I really know it in and out, before getting another one. I stuck with Minion for three or four years; it was one of my first. It took me a long time to get bored with it. I don't usually buy text faces for specific projects, both because of the cost and also because at this point I probably own something that works.

Display faces are usually much less expensive, and I buy them more on a whim. Recently I bought two Laura Worthington faces just for fun, because they looked like they'd be a lot of fun to play with and they were very affordable.

So, to answer, at what point do I know I'm buying a typeface....

For a text family, I have to fall in love with it, and stay in love with it for a long time before I buy it. I admired Brioso Pro from afar for years before I finally ended up with two or three simultaneous projects where I knew it was perfect for all of them, and then I really had an impetus to buy it. I guess, I need to know in every case what I'll be using the font for, but if it's a text family = expensive, it usually takes a lot longer for me to get around to buying it. There are still plenty of text faces — Dolly, Quadraat, Seria, Rialto — that I think are beautiful and would love to have, but I know I'm not going to get them until I really have a project that needs them.

Does this help?

EDIT: You know, my advice to you might be to just go find a font you like, one that's not too expensive, and just buy it. Play with it. Don't worry if you have a use for it. It might be fun to just jump in.

EDIT again: I don't have an older brother, so I missed out on the kissing talk.

Can't help you. I just make the stuff - I never touch it. :-)
However I do feel your pain in a broader sense, since "frugal" is in
fact a big understatement when it comes to my own spending habits...

But you're in luck: it just so happens you have about three
days left to save over $200 on a highly rated fresh design
that I had the privilege of taking part in:
http://ernestinefont.com/
http://www.fontshop.com/fonts/downloads/fontfont/ff_ernestine_pro/
http://typophile.com/node/88349

hhp

I wrote about an extraordinary font shopping experience on my blog.
http://kupferschrift.de/cms/2010/12/font-shopping-part-1/
http://kupferschrift.de/cms/2010/12/font-shopping-continues/

Moreover I would say I’m an impulse buyer but mostly only get a few single fonts if the family is big and expensive. This turned out to be the most practical way over the years for you can build up a reasonable palette which works great for jobbing type kind of jobs and in case you want to use the typeface for complex design work you can get more weights and styles as you need them. This is specially handy with type foundries who offer an obliging update policy where your earlier purchase is credited when you license the whole family later, e.g. Process Type Foundry.

Wanted to thank everyone for their contributions!

For a text family, I have to fall in love with it, and stay in love with it for a long time before I buy it.

I believe that the price for a single weight is reasonable on average. The issue always becomes buying the entire family. I think we as a society are built up to believe that one we buy one thing, we should make it perfect by accessorizing and that's where I can see some of the difficulties. I can't just live with a single weight, because what good would a single weight do?

EDIT again: I don't have an older brother, so I missed out on the kissing talk.

I did too ;-)

@hrant

Simply wanted to say that Ernestine is gorgeous. I couldn't afford it, even with the sale, but I will say that I was on fontshop's website and my mouth dropped when I first laid eyes on it.

Also, thank you Indra for sharing your writing; very enlightening.

Thanks for the compliment (although of course Nina deserves the lion's share).

hhp

I never thought of it as an issue of impulse vs. careful planning.
If there was a typeface that I thought would enable me to create an appropriate setting for a particular job, then I bought it.
The operative word being “create”, because you don’t know what kind of results working with a particular type will produce until you try, you only have a vague and unrealized idea.

You have to choose something you feel an affinity for, which suggests it might help you materialize an idea or effect you’re working towards, which you feel will flesh out the design brief in a way that your bundled fonts won’t.

So there is a trade-off between the possibility that the type you license may not work out for you or the client, vs. the possibility that if you don’t try working with new tools, you will, as you suspect, stagnate.

You have to choose something you feel an affinity for, which suggests it might help you materialize an idea or effect you’re working towards, which you feel will flesh out the design brief in a way that your bundled fonts won’t.

Ahh, Nick my mother said the exact same thing when I consulted her on this issue. She is a small business owner and understands putting down the money for something that furthers the business as a necessity. If you need it: pay first, ask questions later.

But you must understand that I am caught in between that world and another. This other world is the philosophy of producing something very great from very little; that whole "humble roots" spiel, if you will. As an example, a typeface I've lusted for is over at vllg. It is a workhorse serif and I think to myself, whilst looking at the price tag: "Maybe I'm being irresponsible and maybe I can do everything I need to do with Minion and Century. Maybe my inability to produce a creative solution is my own problem and not a lack of assets."

Ultimately, however, I think as a young designer I still am learning that this profession requires we put money into it at various points. Some do it frequently while others do it infrequently. Eventually I'll find my sweet spot.

In the mean time, however, I've since purchased Gibson from Canada Type. My experience with it has been delightful, so that's a good start.