I've said this before (and I'll likely be forced to say it again), but our biggest need on our current defense is speed at ILB and a big run stuffing DT.
Guess what we'd need if we switched to a 4-3? Yep, you guessed it. Speed at MLB and a big run stuffing DT.
So switching would be pointless.
It would also lessen Ware's effectiveness. He's a perfect fit as a 3-4 OLB. He's an excellent pass rusher but is also very good against the run and solid in coverage. He was made for a 3-4 defense.
Making him play 4-3 DE every snap would be like trading away a fortune for Herschel Walker then forcing him into a pro set offense instead of letting him run out of the "I" which was what he did best.
On that note, it annoys me when people say the Vikings got screwed in that trade. The vikings HC was too stupid to use Walker the way he SHOULD have been used. He didn't go from a 1500 yard back to crap in one day. He was STILL a very good runner, playing in an offense that exposed all his weaknesses. If they'd switched to more "I" formation plays they might have won a superbowl. They certainly had the talent (at that time).