Be aware that Poly is easy to get at 7 months out for the time you want. BCV also has a very good chance of being open at 7 months out. Thus, if you want to take a fairly low risk waiting, you could likely spend less at 7 months out since at that time the points from any resort can be used to reserve those rooms.
As noted above, you should not assume you will be able to to get any significant pool time during that time in January when making the choice. You can get some high 70's during the day in Jan but you can also get some low 50's, and those two can easily be consecutive days. More often what you have is mid 60s.. We have been the week you are going about four times and had a total of about 7 days out of the 4 weeks when it was actually warm enough for the pool.
BCV's advantages include walking to Epcot and Studios (or a boat to either), easy access to over two dozen restaurants at the two parks and the Epcot resorts; an excellent seafood buffet, Cape May, at the BC, which also has a character breakfast, and easy access to Boardwalk night life. Poly's advantages include the much larger studio, easy monorail access to both MK and Epcot, and monorail access to rerstaurants at all the MK resorts. It also has a very good restaurant in O'Hana's, which has a character breakfast, and if you want to do the Luau, it is there.
The bus to MK and AK for BCV stops at YC first and then BC and it can sometimes get crowded during rush times.The Poly buses to Studios and AK also have two stops, Poly and GF, and thus you have the same type of two resort delay and risk of overcrowding during rush times.