1. 1:1 swapout is OK if you've done a (comprehensive) Wireless LAN Site Survey. If not, now is the chance to get one done.
2. Do you have a WLC? If you do, you can run 15.4 watts of power on a 1250 with both radio modules on ... here's the catch, the power radius is curtailed.
3. You have the option to use other antennaes and I'll let you know of the links of you are interested.
NOTE: 1250 is not the only Draft N 2.0 AP. Have you considered the 1140? Currently the 1140 is LWAPP only. Autonomous mode 1140 via the IOS will be released shortly.