If the WG act only recieves control pressure to open once the mbc allows, then why do we need to upgrade the thing? Does it just allow room for fine tuning to keep turbo spinning as boost starts to fall?

Do the exhaust gasses ever push the WG flapper open? Mechanically it appears this would take a lot of force.

With stock 10.5 turbo and mbc equipped would there be any benefit to have with stiffer actuator or would this just cause spikeing?

 

Yes, the WG does get forced open by exhaust gas pressure at the higher than stock boost levels. Several sell an upgraded actuator with a stiffer spring just like you mentioned.

The 10.5 outside should actually relieve some of the excess exhaust pressure compared to the stocker, so that the wastegate could stay closed longer, but the stiffer actuator is a good bet if you plan on running boost levels available by using race gas. It should not cause any spiking if everything works right.