First a little background: I've been a casual runner for 3ish years now. Now that I have graduated from college, I have more free time & I'm finally getting a bit more serious, especially about racing. I did two half-marathons during college, off of very minimal training (like, an 8 mile long run was the longest run I did to prep) and on a course with 1200 ft elevation gain/loss. My times were 2:12 & 1:48. These days, I'm a smarter runner & incorporate speedwork, hills (mountains, really, considering where I live), and weight training. I recently had an acute issue with my IT band (related to non-running trauma, not overuse) and am on the mend. Recently I did a 13 mile long run in about 95 minutes. I am doing a half-marathon at the end of May and I'm expecting to complete that around the same time.
My question is this: to really get faster, should I be logging significantly more miles per week? I've never really run any more than 25 miles per week. I see a lot of runners doing at least 40-50 miles per week and some around 85-90. I really want to push myself and continue to PR my half-marathon time. Is adding a lot of mileage advisable or am I going to just end up injured at that level of mileage?