I have flash carts for my Genesis, SNES, TG16/PCE, and Atari 2600. I still keep a fairly large library of quality titles, though. To me, the flash carts are for convenience, for checking out potential purchases, or for playing games that I have no interest in owning. I enjoy having my game library, and wouldn't really consider dumping it and just using the flash carts. I don't have a moral problem with those who do; I just enjoy owning copies of games that I like.
Chris
I'm pretty much in this same boat. I have a fairly large collection of titles across all the systems I collect for, but picked up the flash carts later on (SNES, GBA, DS, and eventually PCE and NES) so I can play some of the titles on real hardware that I have little desire to own, as well as the ones I sort of CAN'T own as originals, such as hacks and fan-translated RPGs.
that said, the big question for me is about SNES flash carts, has anyone here tried the SD2NES?
I've seen footage of it running mega man x2 and x3, which by themselves are almost worth the price of the cart.
No experience with it but I want to chime in here. I'll admit I've used similar logic as you to justify flash cart purchases, but you've got to be careful with it. With X2/X3 you're not paying more because they are better actual games, you're paying more because the physical carts are rare. The JP versions of both carts can be found for under $20, as well as MM7. Of course they can all be played on a US SNES with a minor modification.
(BTW this is also coming from someone who's probably spent more than he should have on flash carts over the years.

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I had about 60 SNES titles when I picked up my Powerpak last month, and had planned on selling one of my pricier carts (Earthbound) to justify/offset the cost. After playing with the PP for a few weeks, I remembered why I collected titles in the first place, and decided not to sell a thing. I've also continued to pick up more titles since then, even though I could've just downloaded the roms and loaded them onto the PP.