As far as GFCI reliability, I've never had one trip via "nuisance". Only time I've seen them trip is when they should be tripping. This usually means your connected equipment is defective, even though it appears to be working fine. You can wait for the small leak to become a big short and trip on over current, but its best to heed the GFCI's warning. To me, the GFCI just gives you earlier warning of the problem. Without a GFCI, you could trip the breaker and still flood the basement because you didn't know it tripped. So you'll still want the alarm to notify when one of your sump pumps develops a current leak.