I flew on SATA business class from YUL to PDL on the 310 last year on the daytime flight. I have flown 20+ times in business on the CSA 310s from Toronto and the planes seemed of comparable vintage.
The service on SATA was better than Air Canada business class, the seats were quite good considering it was a daytime flight. The price difference made it excellent value versus North American fare differences.
The lounge in PDL was very basic - water, pop, coffee and a TV I think.
My wife is from PDL and it was a great visit and I would encourage you to go see the islands. They even have the world's shortest commerical flight with an airborn time of 7 minutes between a couple of the islands.
All in all SATA is on par with many other airlines, the age of the seats and the aircrafts is the only issue but they were in good condition.