There are only two reasons to buy a new bike
1> because you broke your bike
2> becasue you want to <– this is a perfectly valid reason!
Trying to justify it with speed gains, capability etc. is all in your head, unless you’re doing something stupid like riding a SingleSpeed downhill bike in an XC race, or you are already coming 2nd every time and the only reason the guy coming first is winning is because he has a 80g lighter bike than you, then it’s you that makes the bigger difference.
So basically, buy a new bike if you want to, but don’t kid yourself it will magically catapult you several places up the ranking, in fact until you’ve got your setup dialled in on the new bike you may go slower 😉