I did this... I traded in a 3DS for a 3DS XL and got the $100 value. Then, on a separate transaction I traded in a DSi and got $50 (includes bonus) as GS credit. Took a bit of work, but the GS employee really went out of his way to help me by trying a number of combinations on the computer...
How much did you get for the DSi? I wanted to do the same thing, but GS said I can only get $100 towards the XL and no extra bonus for trading in the DSi.
I want to know the same thing, except I want to trade in my psp fat for the new PSP-3000. The coupon I found was $30 extra trade-in at gamestop. Hope it still works!!!
Another vote for the new format.
My only suggestion would be to separate out the games and prices a little better cause it's hard to read. Maybe bullets or something else to signify a game instead of "~".