Not a bad deal. Isn't that pretty much the original cost difference between them, isn't it? Take original list of one and put it against the other. The list on those models was/is public knowledge, right?
I agree with BP that it's a fair deal if you want to trade. A new BX2360 $14368 (Current tractor equal to yours) and a new B2920 $18450 are current prices. The B2920 has less hours. Looks like a fair deal to me if you want to move to a bigger tractor. Yours is probably a bit older being a 30 series than the 2009 B and yours has more hours.
Service charges? As in cost of fluids/filters? The differences in fluid capacities isn't THAT huge. Seriously recommend you do this yourself. It is so easy and you save 50% or more.
As for comparing the tractors, I did a complete review of moving from BX to 20 series B here:
My first tractor was a BX2200 FEL MMM. I had it for one year. Traded it to a B7800 FEL RFM and kept it for 3 years. The B is the next size up from the BX in size, weight, ground clearance and power. The B FEL will pick up more size and weight. The B will pull bigger and heavier implements and the B has higher ground clearance. The B doesn't have a plastic fan for the transmission plus the B has three speeds vs BX two. Some times the BX would be geared a bit to low or high and with the B I usually always used the M gear, could go lower if needed or higher if needed.