...I would base my decision on when you'd rather go, length of stay, and cost instead of the resorts.
Exactly...
Does Stormalong Bay weigh heavily into the equation?
Do you prefer the weather in May vs. August? Or seeing the Flower and Garden Festival (if your dates fall into that?)
Is there more you can do in 8 nights than 5 nights? Do your overall costs (food/tickets/hotel) outweigh the benefits of extra nights/different resort?
If you like the idea of 8 nights over 5... and are just trying to convince yourself that the Boardwalk will be fine... take a few deep breaths and know you're not making a bad decision!
As the previous poster mentioned... there are certainly pros and cons to each resort. The Yacht Club is currently 'rocking' a few fantastic upgrades with their rooms and quick service/sit down restaurant... that the Boardwalk absolutely falls short off. That being said... it doesn't make the Boardwalk a bad choice!
For us... 8 nights would always outweigh 5... and your difference of resorts (Boardwalk over Yacht Club) is almost like a drop in the bucket for such a comparison! Are you having to sacrifice anything for the extra nights? If not... and the idea of a few extra nights of 'vacation' are enticing... than go for it!
Just understand the Boardwalk does lack a 'counter service' that many Disney resorts are known for... and there's a reason they call it the 'Boardwalk Inn'... it's quaint and quiet... and a nice escape from the hustle and bustle of the Boardwalk/Park environment. You're welcome to use the main pool on the DVC villas side of the resort, but as a previous poster mentioned, Stormalong Bay at the Yacht Club will take top honors here. Stormalong Bay also tends to be one of the most hectic and busy pools on property... like mentioned... pros and cons to every resort amenity.
I must say that May has significantly better weather than August... but if you find yourself having a few extra nights, a more relaxing park touring plan, and a bit more time for breaks/pool/resort/water... you could tackle it well!