I'll give you answers based on what Tony and Ralph have said in other posts. They can correct me if I give wrong info.
I'll start with your last question. The free floppy verison of NASLite is the "trial" version. This lets you see what NASLite is like and how you interact with it. Due to the space restrictions on a floppy, the performance is less becuase some drivers had to be left out.
For your first question, because you download NASLite+ there is no physical CD to return like you could do if you bought software at a store. So Server Elements has no way to know if you deleted your first copy or are trying to get a "free" licensed version. I know 99.9% of the people would be honest about this, but it's the others who wreck it for everyone. So the policy that Tony and Ralph have stated is there are no "exchanges" from USB to CD or from CD to USB.
On the other hand, if you can't get it to work, there are lots of people on the forums that are willing to offer suggestions and help. As one of those people

I would suggest you try loading a DOS boot image on your USB key and see if your computer will boot to DOS using the USB key. User edeng has links to the kicker disks in another post so you could search the forums for that post to try them out.
For your second question, if you buy one Server Elements product you can get discounts on other products. I have _not_ heard anyone say this won't apply to a purchase of version 2. This is typical in the software industry. Existing users pay a smaller fee to upgrade than new users pay for the product. What the "smaller fee" will be has not been announced. I have not heard of any 30 day time limit on the discount. Where did you see that?