I just finished reading a great book about how buggy we tend to be when it comes to making decisions and/or judging happiness, intrinsic value, etc. and how irrational we tend to be.
Example--You spend $20 for a theater ticket. You arrive at the theater just before the show and realize you lost the ticket. Do you spend $20 to buy another ticket? Most people say no. Now imagine that instead of the $20 ticket, you had two $20 bills in your wallet, but lost one on the way to the theater. Do you spend the other one on the ticket? Most people say of course. The scenarios are the same--in each you've lost a piece of paper that cost you $20.
Applying similar logic to this scenario:
Many people would hesitate buying another one to build, thinking "Geez, I like this but not when I pay [2x] for the kit". That's faulty logic. The decision to buy the collectible and the decision to buy the build kit are independent.
You inadvertently purchased a collectible kit for presumably regular price. I doubt the market value at the moment is such that you've stumbled upon a huge windfall, meaning you're not likely to be able to double your money on a quick sale. Therefore, the "worth" of this kit to you is the greater of 1) investment potential if you hang onto it 2) the immediate resale value of the kit (windfall gain) 3) the value you paid for what you thought was a build/fly kit.
If you decide to hang onto it as an investment and sell later, or hang onto it because you feel the spark to start collecting for the fun, then the obvious choice is to go out and buy another one because you wanted to build one for that money. I think most in this forum would suggest that as an investment, rockets would be a poor choice. #1's tend to go for a premium, but most other numbered ones rarely command more than a 10-25% premium. As an example, Jay Goemmer's Tau Zero was sold through Semroc. They released a few numbered ones, but he sold the first 25 or so himself and was asking for a little less than double the price. He wound up dropping the price to about a 25% premium because they didn't move.
I personally "collect" a handful of manufacturer's numbered editions, but not so much because I expect them to go up in value, but more because I take some measure of pride in being one of those firms' best/most loyal customers.
I would, though, suggest that unless you really want to start collecting, just hanging on to this one lonely #2 is not going to be much fun, so either build it or turn it right around in the yard sale here to try to get maybe 10-20% more than you paid, enough to cover a BP motor. Then take that money and go out and buy something (another one of these?) that you'll enjoy building. I don't think I'd build this, though, as you could probably get slightly more money selling it.