You need each leg of a 3 team 10pt er to win more than ~82% of the time to win at -120. Ties typically lose on 10pters too. 5dimes only charges -110 on these so -120 isn't anything special.
So if the original bet was 50/50 you need those 10 extra pts to matter more than 82% of the time, which on totals I doubt it ever does. Any extra pts you are getting from the stale lines is probably better used just straight betting them. The teaser wont increase the ev, it might lessen it though.
On sides you could probably finds some way to take advantage of stale lines with teasers. If say he has an NFL game at -6.5 and the market has moved to 7 or 7.5, I would imagine +3.5 would be a good leg. Or a -2.5 that has moved to 3 should be good going to +7.5 the other way.