I have one of the original line PSPs, so it's not an option for me, but it almost makes me want to pick up a slim.
You could get one of those PSP2TV kits, but they're not exactly the best solution in the world (they drop a few lines... + the 16:9 option cuts even more lines than the 4:3)
I have one and use it for some random crap every now and then. (I actually first got it for use with Radiant Mythology while I was having some hacking fun with the Japanese version, before the US version was announced). I might get a Slim later, but I need some different capture equipment or some sort of magical pass through device to pre-process/crop the image to fit my entire screen (both for capturing with some old non-HD equipment and viewing pleasure)
Anyway, unfortunately, unless the price has dropped for the PSP2TV kits, I guess you'll have more of a personal profit on just selling your old PSP and getting a PSP Slim.