Try the locking the body copy to the document baseline. I always define this in the paragraph styles.

...is this sort of visual hierarchy advisable?)
You might want to consider upping the blockqoute, but this all depends on the style you are after. If they are more important than the notes they should get more attention. The New Yorker have smaller quotes in text, btw. It works quite nice for them.

Are you using Minion’s optical sizes?

I suggest you to read this book:
http://www.amazon.com/Detail-Typography-Jost-Hochuli/dp/0907259340

Yes, definitely lock the main body text to the baseline grid. Don't drop the point size of block quotes. (I know this is very typical, but it's a Victorian custom with no real benefit; simply indent both sides of the quote to match the paragraph indents, or set in italics or sans serif or something; no need to drop the size.) If you disagree and do end up setting the block quotes smaller, incorporate a blank line as a "space before" option in the style, then manually baseline-shift the whole quote to visually center it between the line above and the line below, the position of which will be determined by the grid.

Thanks for helping out a newbie, y'all. :)

@frode frank: Sorry, this is actually the first time I've heard of the term. How do I find out if I can use the optical sizes?

@Frank Adebiaye: Thank you for the recommendation. That's definitely on my to-buy list.

@Joshua Langman: I decided to set the quotes in the same size, though for future projects I'm trying out your other suggestion to see if I interpret your instructions correctly.

As you can see here Minion comes with a multitude of versions. I’m refering to Capt(ion), Disp(lay), Subh(eader). These are, in addition to the normal version the optical masters. Each version is intended to be used at a specific size. You’ll have do some exploring yourself, but the idea is to have a page of even color across all sizes. A good optical size also take into consideration the typical needs for it’s intended size. This might include changing the cap-height, x-height, ascenders or descenders length, spacing, width, weight, trapping, degree of openness, etc. One size does not really fit all, even though digital makes it possible.

@frode frank: Apologies for the late reply. Yes, I'm familiar with those; I've used them on past projects without knowing they were optical masters. Thanks for clarifying that for me!

Block quotes one point smaller than the main text and indented is a standard practice, and will look "normal" to readers. I'm not sure if it's wise to have your baseline grid any finer than 1/2 your normal text line size (point size + leading). You want your bottom lines on facing pages to line up. When I did this recently, I didn't lock the block quotes to the grid, but let them float, and made visually equal space before and after. Maybe there are better ways to do it, but that worked.