Optical drive lasers (and the Wii's drive follows the same principles as any other DVD drive) are not worn out by certain media, they're worn out through use. Bad media will cause lots of retrying when the drive can't read a crappy disc, leading to it having to do more for reading the same data - leading to it wearing out faster.
I don't know of any particular problem with the Wii's drive reading +R media that would cause it to have more difficulty than with -R - the issue with +R media with the Wii's drive and DVD drives in general is a firmware compatibility one, one that is largely fixed by setting the booktype to DVD-ROM instead of DVD+R.
The Wii's drive is more picky about burned media in general than it should be, and I suspect your media isn't very high quality. If you're paranoid about your Wii's laser, use good quality discs (e.g. Verbatims or Taiyo Yudens.) Otherwise don't worry about it, +R or -R, as long as the Wii reads it OK.
