I don't think this is necessary.
Moderators' rate limits are removed in a number of places where it could potentially be necessary to fulfill duties as a moderator. However, everything else remains functionally the same.
Since bounties aren't related to being a moderator, there isn't a pressing need to increase the number of available bounties for moderators.
In response to the edit, I think you have an interesting idea on the use of bounties. While I can see how bounties could be used as a moderator, I still don't think it's necessary to raise the limit.
- This type of modeling is the same type the community can do already. While drawing attention to examples of model questions/answers is a good role to take on as a moderator, it's not critical to the moderation process.
- Are the questions you're putting bounties on really examples of truly model posts? Most sites - even Stack Overflow - don't receive truly phenomenal posts with particularly high frequency.
- You can already give 1500 reputation per week out with the bounty system. Unless you're a bona fide wizard, consistently earning more than 1500 rep/week is phenomenally difficult on most sites.
- Constantly giving out bounties decreases the significance of the bounty system.
I might instead suggest rewarding bounties on the occasional spectacular answer? Or, perhaps, keeping one bounty out to acknowledge and draw attention to something in particular you think people would be better aware of?
While I think you've got an interesting idea for encouraging specific behaviors, also remember that the significance of a bounty decreases the more of them there are.