Is it worth buying a road bike or rather upgrade mountain bike?
Only you can decide if you &quot;need or &quot;want&quot;  a road bike. I would not upgrade your mountain bike in an attempt to make it a better road bike. As the saying goes a pig wearing lipstick is still a pig. If you want to road ride for a change of scenery or pace buy a used quality built bike. The used market should have lots of bikes suitable to the local roads. Your times will improve over the MTB on the road just from the gearing alone. If you shopped well,  after a year  you can decide if you want to upgrade or just sell it. You should be able to get 80% of what you paid for it. If you buy a new bike you might get 60% of the much higher new bike cost a year later. I would ride the mountain bike  until the bike becomes the limiting factor in your race times or it breaks. If the races you ride are competitive just upgrading your MTB won't move you from 25th to 1st place conditioning and training has to come in to play.