TSA has absolutely nothing to do with this. The rules in place are DOT's. Those, just like DL's own COC, require that the value of the bag be reimbursed.
The value of a three-year old bag for which you paid $300 is likely way, way less than $107, unless it really has sat unopened in your closet.
The funny money offer of $200 is useful if you are a regular DL flier and can use it. The reason DL offers the vouchers is that the "breakage" on those is high and most are simply never used.
If you can document a higher fair market value for the bag, then you are free to try, but I think that by any measure, you have done very well and should take the money and run (deposit it).