What Watch X? Nothing has been announced. So your options are to do a battery replacement on the S5 or get a newer watch. Only you know how the S5 fits your needs and how the S7/S8/S9/U1/U2 might fit in there too.
The economy probably needs more consumerism so I’d say buy it. But it’s probably something that you need to spend a little time weighing up the pros and cons. What is it you like and don’t like about the S5? I’d start there.
Or just go and buy the Ultra 2.