If it isn't broken don't fix it. Getting stronger either in the low rep range or higher is still a strength gain.
If you do want to handle heavier weights I'd say the 3-5 rep range is heavy enough (not going to failure) and then follow with some back off sets of 8-12 for volume. Most people aren't ready to do heavy singles and it be more beneficial than higher reps.
"...I have found the Iron to be my greatest friend. It never freaks out on me, never runs. Friends may come and go. But two hundred pounds is always two hundred pounds." - Henry Rollins