Do It, Maan...
Good speakers have a long shelf life. A few years ago I decided to choose a speaker line that was discontinued for a few reasons:
1. Current speaker line equivalent wasn't as impressive IMO
2. Discontinued speaker line was more attractive than current equivalent (again, IMO)
3. Cost savings on "last year's model" was significant
If you're trying to decide whether to complete your set w/speakers that are all from the same line but are discontinued, that's likely to provide you with the best chance at timbre matching than mixing and matching lines, though most speaker manufacturers will try to keep previous models of the same caliber fairly well timbre matched. Similar to what I've noted above, this will likely yield you savings than the current line available as well... -TD