1. Changing RAM in a 10v is a serious endeavor. It requires disassembling the the lower part of the computer.
2. Based on reports in this forum it seems that more RAM will definitely make your 10v run hotter but the reports are mixed as to whether it speeds it up. Commonsense would suggest that if you don't keep lots of apps open, or don't edit 500mb images in Photoshop, you can probably get by with 1GB of RAM under Snow Leopard.
My 10v has 2GB of ram because that's the way I ordered it (it came with Linux...you can't get 2GB with Windows). I've been constantly checking Activity Monitor to see how much RAM I'm actually using in Snow Leopard. I use Apple Mail, iTunes, Firefox, VLC, OpenOffice and GIMP (with relatively small graphics files). I haven't gone over 1GB so far.
For anyone still using Leopard, the one thing that does speed up a 10v (or 9) in a big way is upgrading to Snow Leopard. I have both a Mini 9 and a 10v. In both cases, the upgrade to Snow Leopard produced a significant speed gain.
My best advice is to check RAM usage in Activity Monitor when your computer begins to slow down. See if there have been any Page Outs. If so, you will likely benefit by adding RAM.
If your Mini gets really hot, I believe the Atom chip will automatically slow down (not sure about this). If your computer is really hot and slow and there haven't been any Page Outs, then the heat may be a factor.