My understanding of the new formula:
Completing an optional research tech does not effect tourney squad sizes. Your regular squad size no longer effects tourney squad sizes (that's what increases when you take the optional SSU techs and was what used to cause increased tourney squad sizes). So taking them will have no effect on the tourney; it won't make it any more or less costly in troop resources. Taking them will help on world map province fights since you can bring more troops into the battles and the enemy squad sizes are established when you complete the Advanced Scout tech for each chapter. Enemy squad sizes only go up by a small amount each as you clear more provinces until you reach the amount needed to open the next chapter Adv Scout tech.
Taking them will also help with certain AW bonus, ex: Dwarven Bulwark. Both the number of light melee units produced and the Training Size added are percentages of your regular squad size. In my case (Ch 15 city), I stopped upgrading the Bulwark once I got the Shrooms. Increasing one AW level has the same effect on the tourney no matter which AW is upgraded. Since the Bulwark now requires way less kp (590) than the Shrooms (920) for the next level, I may decide to start taking the SSU techs and upgrading the Bulwark. Since my Shrooms are at lvl 19, I'll probably get them to the next rune upgrade first. Either way, I decided not to enter Ch16 months ago (nothing there I want) so even though I've got the kp filled in all the SSU ones I skipped, I'm going to save them for 'research a technology' options in event quests. It's been forever since I could take advantage of that option.