I have a 1DmkII and still use my 10D as spare for sport photography. IMHO the 20D is not that much of an upgrade over the 10D as people like to think and that is why I have a 1DmkII.
IQ, 2 MP is barely, if at all, noticeable.
Start up is slow, but who shuts their camera off all the time while they are using it.
Buffer is only an issue if you shoot consecutive in RAW, not an issue in Large JPEG.
AF is the same as 20D.
10D doesn't and never did have battery grip issues.
High ISO noise, 20D is better no doubt, but 10D is still acceptable. Not a real issue unless you are going to shoot 1600 and 3200.
If you are trading straight across its worth getting the 10D, but if you are throwing money in, go right to the 30D
I loved the 20D, 5fps, almost instant on (far more instant than my 300D.) I don't turn off the camera, I left it switched to on, I just have the camera auto turn off after 1 minute though to save batteries. It's not an issue when I'm continuously shooting because the camera goes right back on. With a slower camera you have to leave it on all the time or you might miss a shot while you're waiting for the camera to turn on.
Also, I always shot in RAW, I had the 20D with a 1GB SanDisk Extreme III CF card. When I switch to a slower memory card (I had a SanDisk 256MB CF card that I used mostly for my Powershot G3 when I had it) it was painful waiting for the buffer to empty and I dreaded having to use that card. The thing is, the 10D will be fine, unless you one day pick up a 20D and start to use that for an hour. Just like cheap glass is fine, till you pick up a 70-200 F2.8L and then you don't want your camera touching anything without a red ring on it.