Is the Infini-Lift Lightspeed worth it?

In a word: Yes

It is so incredibly fast. Even better, it's much easier to actually stop at the target floor (even if it's floor 2). For some reason, it's also easier to read the floor numbers. (Personally, I also think it looks better than the previous elevator, but that might just be me.)

It does take a while to save up for it, but I would definitely recommend it.

Yes, definitely. I actually would recommend not even getting the gold elevator until you have enough bucks to upgrade to the infini-lift lightspeed right away, because the gold elevator has such a frustrating stopping distance.