And also, what programs push the RAM to the limit? If the DSP's gonna take up a chunk of the RAM, then some things might need a swap file in the near future.
I was running Midori with 2 tabs open, an audio player (I think it was Exaile, but pretty much any could apply), running SNES, with a fairly large PDF (or did I have two open?) displayed, and (attempting, it was really slow by this point) to play Big Buck Bunny in VLC, and I still had about 20MB of free RAM.
Outside of opening a bunch of tabs in a web browser, there isn't really a lot pushing the boundaries of RAM at the moment.
I suspect Mupen is one of the closest to filling it out, but I can't figure out how to get back to a desktop and test that while it's running.
Having a swapfile with swappiness of -1 is probably not a terrible idea: it'll sit there unused at worst, and in the unfortunate event of needing more RAM than is available, it'll kick in to help. On the other hand, by providing swap, it can mask a problem in the way your system is running: you might find one day that your Pandora is running kinda slow and have no idea why, unaware that some process has gone and sucked up 400MB of RAM for some stupid reason.
So maybe a trade off: just 64 or 128MB of swap against the Pandora's 256MB physical RAM; that way if you are running a bunch of stuff and butt up against the extents of RAM, you have an emergency buffer, but at the same time it isn't so large that some crazy process can run away with huge amounts of RAM and leave you with a slow system.