Personally, I'd go for option 1. I don't believe that a tent is nessecary in any season (bar arctic conditions). A tarp can be rigged in many different ways to creat a completely weatherproof structure. It is also much easier to use it in conjuction with found and natural materials to create a more sturdy shelter. It is also less conspitious and easier to repair.

However, having a tent is nice and a comfort to have, espessially in bad weather, and as you have bought it specially, I would change my BOB to suit the time of year.

(Sorry about the spelling)