If you’re looking for just filesharing capabilities, OwnCloud might be a good alternative. It’s recently been rewritten in Go and its supposedly quite fast. I must say that I haven’t used it myself.
Another alternative could be Nextcloud, but that comes with a whole suite of other software such as calendar, contacts, …
I’ve also heard some good things about seafile, but never used it myself either.
I think buying a larger drive would indeed be the safest option.