The part that kills BPs as an investment is the overhead. Being able to buy an animal for X and then sell for Y for years and years sounds great until you figure in how much it costs along the way to keep the animal.

If you aren't breeding in large numbers or don't breed your own feeders, the monthly costs of just maintaining the animals will eat up a lot of any profits you'll see down the road. You can't be paying $2-3 per rat per animal per week and expect to make a profit hatching out a couple of co-dom clutches every year, maybe unless you are dealing with morphs that are still going for $1-2k each...

I buy my rats wholesale and estimate that it costs me about $100 per animal per year to maintain. Buying feeders and supplies at retail will set you back 2-3x more. This is always an important aspect to factor into your breeding plan.

Basically, what I'm saying is that you have to reach a certain economy of scale in order to really call it an investment. Otherwise, don't spend more than you can afford to lose, and just enjoy keeping them for the sake of the hobby.

And as far as selective breeding goes - nicer animals are always going to sell faster than crappier examples of morphs. "Selectively bred" animals are going to be a marketing tool used by sellers to get more for what they produce - and rightfully so - animals from strong lines are going to be better than those that are not. And then again, what is considered to be a "nice" specimen is very subjective anyway. Best you can do is buy animals that appeal to you the most, regardless of what the seller thinks.