I actually disagree. I'd like to see the extra point be hard enough that going for two becomes a viable risk. The two point conversion success rate is usually somewhere in the 40-45% range. I'd think making extra points more difficult, to where maybe they were a 75-80% chance would be enough to see more teams go for two. but not so many that it renders the XP unnecessary.
I think I've seen numbers as high as 52% for two point conversion success rate. 90% conversion rate would make two point conversions pretty viable. 95% isn't bad either. Although coaches are always way to conservative even with statistics proving them wrong.