I've almost never sold tickets for an event I didn't attend because most of the time the tickets weren't expensive enough to make the hassle worth it

That said, how much of a difference does it make if I sold my Brazil/Mexico soccer tickets at Kyle Field now versus a week prior to the game?

I want to hold on to the tickets until the week of the game just in case Aggie baseball doesn't host a super regional/or heaven forbid doesn't get out of the first regional

(The soccer game is the same as super regionals)

IMO there is always a market for tickets.

Personally, I am assuming that the baseball game will be early and soccer later (aka double header).

Also, there appears to be plenty of tickets available so the resell market may be soft unless you cut your price.

In my experience (I buy a lot of tickets on the secondary market, Aggie sports and concerts) - the best time to buy is a few days before the event. Sellers are more motivated and prices drop. Usually people will post them early at the "want to sell for" price and hope that someone who is not as price sensitive but just wants to secure the tickets early will pay it. Also, people's plans change at the last minute for various reasons and they just want to get some of their money out of the tickets.

YMMV