Beside the fact that flash memory has a limited amount of time data can be erased-written before it wears out...
So erasing games on the Wii memory and reinstalling them like you used to do is somehow better?
Boy people do complain about anything. Oh noes hacked Wii owners may have a broken homebrew channel, what shall we do?
In regards to demos, I doubt it in regards to Wii game demoes because you still have to deal with the internal memory since it sets aside a chunk of that memory for this feature depending on the game size. You may be able to double the size limit but beyond that there isn't much wiggle room when you only have 512mb total to work with.
About speed, everything seems to run really fast for me, maybe the problem is that you are using a slower SD card? It takes like 6 seconds for me to load the SD channel and 10 seconds MAX to load any game on it.