Hi Rose,
I have been to Cuba several times & have stayed at the Plaza more than once and found it fine. It is in a super location right in the heart of the old town. There is no pool but there was an arrangement with, from memory, the Sevilla! so that you could use theirs.
Re the Tropicana I have never, in 8 visits, felt the urge to go there and do not feel that I have personally missed out. Others I have spoken to who went said they really enjoyed the night out. Is it, to you, worth the money? Last time I was there this excursion was combined with a ride in an old American car (these are now generally all taxis and are all over the place so you could ride in one on your own - just hold out for "Auto Americano") and stopped at a statue of John Lennon (which incidently I told TS about on a trip many years ago & has been on their stops ever since) in Vedado which you could easily do on your own - perhaps in that old American car.... Prices are erratic - but not excessive. Just agree a price before you set out.
Have a great trip.
Ian