In what ways is it a better experience? What are the benefits?
benefits are mostly what he said. base leveling scales per level so it's a lot faster to get 2/4 platforms than 4/4 platforms, so in general you'll unlock items or field support faster in SP by upgrading MB and FOB at the same time. plus you can get rewards from the virtual battles, the challenge upgrades, or just FOB raids...
that said, most of it is just about items or field abilities, and those are just bonuses. I turn a lot of that off now... I rarely use field support abilities, and actually often use level 1 weapons just to make the game more fun. play with Marking Off too so some intel stuff is lost on me. so the "benefits" are a nice bonus but not really important.
"better experience" i guess is subjective. i think it made my experience a lot better at first because I think the FOB concept is pretty cool, and I liked having another base to build up. it helped make my resource gathering feel a lot more meaningful. it was just kinda cool, too. I like the general PF theme to FOBs.
that said, a lot of that was lost after the first few weeks once I beat the game, Konami started changing FOB upgrade balance, etc. which is all the more reason why FOBs 'best' moments are probably when you're still mostly in the single player between missions 20 and 40. when you're still immersed in the 'story' and in that 'honeymoon' period is when FOBs feel the coolest.
which is why i think it's not a good idea to try 'save' them because they longer you wait, the more SP (or roleplay, story) appeal they'll lose and the more end-game-y/grind-y they'll become.