Well that certainly takes the pressure off you, because they'll accept USD anywhere in T&T - so if you need to buy anything at POS airport before your transfer, you will have the means. As regards spending the USD, it all depends upon how 'keen' you are to get rid of them. Remember, whilst people may gladly accept USD (or any other currency) they are not going to give you the rates you could expect from a bank - and lets be honest, the banks will fleece you dry at every opportunity. So, every time you change money, you lose money. But, if you've got it and don't envisage any short-term opportunity to use it in the States, where obviously you will get maximum value per buck, then use it. Hope that all makes sense!
Have a great trip, you lucky so-and-so!