Okay, so I've always had problems keeping my stitches consistent through my seam allowances. I can reliably get 6-7 sts to the inch in the rest of the quilting, but when I hit the seam allowance (especially if I'm sewing along it), I'm lucky to get 5! What I was wondering was, 1) Would it help if I pressed the seams open so I'm only adding one layer of fabric there, and 2) Would it make much difference elsewhere?

I don't hand quilt, but I do machine quilt. I have learned that on some patterns I open the seam and it makes it easier, so it may be the same with hand quilting.

This is my solution:

1) Plan your quilting designs to minimize crossing seam allowances

2) Use a stab stitch when crossing seam allowances

This is what I do. Especially 2)

After hand quilting an irish chain diagonally through all those little squares, I asked everyone I could think of about this. I can not do a decent stab stitch to save my life, you talk about crooked, oh my! I found one more way to deal with this problem, I hope I can explain it in such a way that it will make sense to you. When you come up through a thick part and don't like the large space between your last stitches, instead of continuing in the same direction, go back one stitch and rock forward normally just one stitch at a time until you are back to the normal thickness and small stitches. I was sure that it would result in double stitching on the back, but it doesn't. It is the only way I can get through seams. I will in the future be much more carefull in planning quilting designs to avoid seams. If this makes no sense to you let me know and I will try to find the book that will explain it better.

Roselady:
Roxanne McElroy describes that technique in her book "That Perfect Stitch" . I've used it many, many times and it works perfectly for me!
I am a lucky person because my wholecloth quilts don't have any seams or only one or two where I sew the length of fabric together. I press the seams open so I can cross them with a regular quilting stitch.

Roselady, I do exactly what you described in hand quilting over seams. I often try to plan my quilting so I can avoid as many seams as possible, but with many it just istn't possible!

On an Irish Chain, I've combined both hand and machine quilting. Did the machine quilting over the areas with the most seams and the hand quilting in the more open areas. Looked good and held up well.

pressing your seams open for hand quilting is perfectly acceptable...anything to have less bulk. and in those areas you may find it easier to get the small-consistant stitches if you (stab-stitch)that area instead of loading numerous stitches on your needle.

I don't worry about it.

Sometimes I'll do a back stitch to help shorten the distance between stitches, sometimes I stab stitch, but even these methods don't look the same as my regular hand quilting. It's not the end of the world if these stitches aren't the same as the others and a lot of times I just do my best and let there be space between the stitches.

Since I really like to hand quilt, I pick projects that have open spaces and not so many seam allowances. I wouldn't hand quilt a Bargello or log cabin quilt - to me, they're perfect machine quilting candidates. I did hand quilt a king-size Bargello for a friend, and it was torture!