It's not something that should be encouraged, but if the game is fun you shouldn't refuse to buy it because it has (really really) bad graphics.
The way I see it, PSP ports are better than nothing at all. I have two games that also showed up on the PSP, this and Heatseeker, and I enjoyed them both. As long as they improve the gameplay, which they did in both instances with very cool controls, and it's good, I buy it.
The developers (read: publishers) won't take poor sales as signs the game wasn't good, they'll take them as signs the Wii userbase doesn't want games like this and go back to making safe minigame collections. On the other side of that, if it does moderately well it may encourage them to put more effort and resources into their next Wii project.
I'm not saying rush out and buy every PSP port, but you shouldn't automatically dismiss a game because of that either. Nintendo has the attention of all the third parties right now, it would be best to try and retain that attention. This is a solid effort in everything but graphics. If it does at least moderately well we may keep the publisher's interest long enough to get another game, hopefully designed from the ground up on the Wii.
We haven't really seen anything like that yet, everything so far has been ported from something or another at some stage of development or been merely a minigame collection (which have their place too, I have and enjoy Rayman and WarioWare, but I don't want every other game on the console to be minigames). Mario Strikers was most likely Wii the whole way through, and it looks significantly better (graphics wise) than anything before it. Then Metroid comes next month. A game that proves the Wii can do a great action game, that it can do something epic, and shows that the machine is hardly a "GameCube 1.5" in terms of graphics.
If we can talk a publisher into letting a developer do a fullblown Wii exclusive, which shouldn't be too hard when you show them the sales figures, we'll see what they can do. If a publisher waited til the Wii was a bona fide hit and then started development on a real huge game it will be at least a year before we see it. This year we've got the (hugely great) showing from Nintendo and a few third parties who realized what Nintendo had on their hands soon enough. People have said Nintendo doesn't have much themselves next year, using all their aces this year. The strategy will work because by next fall we'll start to see what real third-party games that started life on the Wii can look like and play like; Nintendo won't be as needed because the third parties will start to shine.
Sorry about the rant, I just think that Nintendo has been hurting in the third-party area since the SNES, and we've finally got them back. Don't screw it up.