I would suggest spend it on energy refreshes for gears especially on the higher gear levels. Focus on one toon you want to gear up. I know some beginners that spend that on multiple toons which isn’t effective for you after 3 years. Use the energy refreshes on Easy nodes which will net you better chances than the hard nodes which requires a lot of energy. It would take you months to build up enough crystals to buy a 1,400 crystals gear pieces. I think most of us spend it on energy refreshes.
I would suggest try to get into 200-ish in the squad arenas and ship arena to get shards for the shard shop and zetas in ships store every two days. Sometimes you’ll find high levels gears in the shard store are valuable.