I've certainly considered doing this for some of the pricier games... Not just SNES/SFC, but also NES/FC (since I have a FC and will get a Retron5) and Genesis/MD.
As it is, though, the only import games I've bought online are Gokujou Parodius Da and Zero Wing, neither of which didn't get a US release.
The rest of my "imports" I actually bought in Japan, bought off my friend who went to Japan with me, or were given to me as a gift... in Japan.
I've found a couple things when looking for imports of expensive US games, though...
For one, although they can often be cheaper than the US versions, the rarity of the US versions can drive up the imports' price as well. A Japanese copy of Seirei Densetsu Lickle will certainly cost less than a US copy of its counterpart, Little Samson, but that JP copy will still normally run you at least $70. PAL copies of Stadium Events especially suffer from this dumbness.
Also, there's an issue of pirates, particularly on the Famicom. They're plentiful and can look pretty close to the official cart, especially if you don't research ahead of time what it's supposed to look like. Biggest tip-offs can be badly stretched art, lack of copyright blurb, and odd cart color (pirates are often soapy pastel colors for some reason... probably cheaper)
And most sadly, sometimes the rare games are even more rare or non-existant abroad. "Maybe I'll save some $ and get a Famicom copy of Flinstones: Surprise at Dinosaur Peak" = Nope, doesn't exist. Except as pirate carts.
