The value for any account its UA is in effect an accumulation of all following accounts their UA, that depends on their UA, which is an accumulation of their followers UA etcetera. Do you consider it to be a needed part, using it in combination with SP?

Nope, high-SP is correlated strongly to high-UA, but only as a side-effect:

• people follow high-SP accounts (for notifications, and to get rewarded via commenting)
• people also follow low-SP accounts for good content (I value each of my own followers as gold...)
• ignoring SP into the UA matrix, allows for jailing accounts in the follower matrix (ignore all from-to follows regarding accounts X and Y)
• UA allows for Democratization of Steem, because many small accounts can collectively decide to unfollow accounts X and Y, effectively taking away their powers:

ref. Proposal HF 22: vote_reward = UA * SP