We’ve done split stays a few times (usually to save money or because we wanted to sample other resorts). Honestly, I only find them appealing when we have a longer stay because of the obvious disruption with switching. That being said, if you don‘t have much to pack up and move, it’s not a huge deal. We have kids so that makes it more work. Disney is really good about moving you, so with just two adults it would be an easy transition.
Since you plan on spending a lot of your time at EPCOT & Boardwalk, BWI is a great choice. Being able to walk to EPCOT (and DHS) is everything. We love that resort so much. It was one of our best trips ever. Be forewarned that they don‘t have a food court, but they do have pool bar with some food and a bakery and walk up pizza window out on the boardwalk. (FYI- not as convenient, but Beach Club food court is a 5 min walk).
POP is a good pick if you’re trying to save money. We’ve stayed there twice. Fun, clean resort and now with the refurb and SkyL, even better. My suggestion with all things considered is either do a split stay with 3 nights at POP followed by 3 nights at BWI OR all 6 at CBR like you stated. I know that probably doesn't help, but at least I’m agreeing with you! So I guess you just need to figure out how bothered you’d be packing up mid trip in order to stay at BWI. I think it’s worth it. Have a great trip.