Cruise NYC-Caribbean

I’m new to the forum and I would like to ask for your advice. Mrs HH and me will go for a cruise October/November 2016 from NYC to the Caribbean. We live in Kuwait and consider us as regular, but not frequent flyers and usually travel in WT+/CW or equivalent with the likes of BA, LH, EK. I would like to spend as many Avios as possible (250k) available for an upgrade from WT+ to CW because that seems to be the best option to spend Avios, right? We have no particular FF status.

I checked the BA website and they offered outbound flights from KWI to JFK via LHR in WT+ and inbound from PUJ via LGW to KWI in CW for approx. GBP 4500/- for the two of us. Outbound and inbound we have stop overs (1 day/2 days) in London. We feel that is more convenient.

Given the regular CW rates for KWI-LHR-KWI it sounds too good to be true. Even if we wouldn’t be able to upgrade for the day flights from KWI-LHR and LHR-JFK WT+ to CW it looks pretty good. Any thougths?