What kind of riding is your current bike holding you back from? The biggest thing to consider to make the most out of the N+1 bike mentality is to try to minimize the amount of capability overlap between bikes. You mentioned being interested in possibly racing DH/Enduro but your current bike would be a perfectly capable enduro racer and would be more than adequate for lower-level DH racing (at least enough to see if it is for you before taking the full plunge) so you’d have a ton of overlap there. If you have a lot of more XC-ish trails in your local area that your current bike makes feel boring, I’d say a HT is the way to go.
For example; I have a YT Jeffsy for more aggressive trail riding/ light park days (I’m on the wrong side of 40 and don’t get too aggressive or ride serious DH anymore), a steel XC hardtail for trails that are just a bit much for a gravel bike but are pretty boring on the Jeffsy, and a fat bike for winter. They maximize my capability for riding I’d want to do while minimizing capability overlap.