It all comes down to what your main uses are.
Emulation - probably not so much. Emulators don't write to the card much. Read speed is really more important here.
Homebrew - probably not so much. Like emulation, not a bunch of writing going on here, but resource heavy homebrew might be doing a fair bit of reading.
Productivity - Might be worth it, especially if you save and load many documents frequently.
Connectivity - It might help, if you're caching pages to it, but not by much.
Media - Here's where a fast card matters. If you're changing out video often, a fast card will save you lots of time. An Season's worth of hour long tv episodes is a lot of data to transfer. If you're swapping out gigs of tv often, a fast card is nice.