Perhaps it would be useful to post what your travel patterns are, not just for next year but in general. For example, where are you based, and where does most of your travel take you to? This will help everyone here give you a better answer.

My first thought was that perhaps you might be better off pursuing status on one of the foreign airlines you’re traveling. UA status (particularly silver) typically has limited benefits on other airlines. You’re also at a disadvantage earning UA status due to a lack of PQMs on those carriers depending on how you book your ticket.

I agree that spending $2,100 to get to silver before the end of this year is not well advised. You’d be better off paying for checked bags and economy plus until you get to silver through your regular travels.