Size, yes. Absolutely. Price and promo, no. You can try to wait for a better one but they keep raising base prices. We bought 105 direct for our first purchase. I believe that you can get 100 on any locations currently having a promo (Aulani, AKV and BLT) the rest I'm not sure but you can ask. I don't think you can get under 100 for a first time purchase. Most promo prices will be tied to a minimum (and under 120 or 160 probably won't have a promo) so be aware of that and in general the sold out resorts aren't offered for promo but are often available to buy direct if you ask. You might be able to negotiate a split contract if the total equaled at least 100 though, not sure.
Beyond that all you can try to negotiate is UY and banking points. So for example if you are buying in the last month of a UY you can make sure those points are banked even though it's past the banking deadline, which basically gives you 4 years worth of points to play with almost immediately, and one of which the dues are already paid. Not really a negotiation but just making sure you get the max potential value of a direct purchase.