I still have my oneplus one? Time for an upgrade?

I had the OPO, then the OP3 and now the OP5.

The difference is massive and I'd say it's worth the upgrade if you use your phone quite a lot. However if I was in your position now I'd wait a few months until the OP6 is announced.
Then if there's any new features you like the look of on the OP6 you can get the latest and greatest, otherwise you could pick up a OP5 at a reduced price.