CSGO does this as well, if you play casual on csgo you don't get nearly as much xp as you do from a game of 5v5. Make it the same way in sandstorm. If you do this, it will bring more people to the competitive gamemode, and at the same time give people more xp, which they have been asking about for a long time.
Yes and no. I hope people play competitive because they enjoy competitive and not because they wanna play with barbie dolls. Just joking a bit, though you get what I mean.
It might attract people obsessed with points and therefore more cheaters as some people dont really care about what should be the core of competitive gameplay imo: Outsmarting real human controlled opponents with your team and having a fun challenge against enemies way smarter, resourceful and imaginative than bots.