You must have a really big garden lol. Based on the size of your abode you obviously can easily afford a $8K bike so just enjoy it. It doesnt matter if its under uterlized now as long as you know you will use it when you have the mood. I was crazy about biking back in the 2000s then left the hobby after i was working overseas and now back in the biking hobby and just bought a road bike. I also asked myself if i did the right thing in buying a >$2K bike (all my past bikes are below $1.5K) but i have a good track record in cycling as a hobby throughout my life so i think its worth it. Unless your interest was just a fleeting one or you have totally lost interest.
Once bought everything drops in value even if its a one week old item. If can sell then sell, if cannot sell just keep it.