I tend to disagree. I think it depends on how much you can sell your 8500le for and whether or not you can find a quick and ready buyer. I would imagine $40 for a good used R8500le is not unreasonable and would result in a quick sale. The end result is that this "upgrade" would only run you $25 and I think that's definitely worth the effort.
Speaking as an owner of both a retail, 128mb R8500 (full 275/275 speed) and a 64mb GF4 ti4200, I can say that the ti4200 is (very) noticably faster than the R8500 in almost every way. Even overclocked to 301/301, the R8500 cannot compete against it. The only area where the R8500 is superior is DVD playback, which is ATI's greatest strength.
Don't get me wrong, I still love my two R8500s (in fact, I have a 3rd, used one coming in from e-Bay), but if you're a gamer, the performance gain is well worth the relatively low cost (which I don't think is high enough to prevent you from getting another upgrade in the near future).