If you've spent two years in the sixty mpw range and stayed healthy, then, sure, bump up the mileage a bit this winter. You should take about a month-and-a half to two months to build up from wherever you usually start mileage-wise to a peak week of 70, not incorporating anything faster than threshold pace (30s/mile slower than CURRENT estimated 5k race pace) other than 6-10 x 75-150m strides 2-3 x week after your easy runs. I wouldn't do anystructured workouts during this time, sticking to aerobic fartleks, long hills, and cutdown runs (using effort as your gauge rather than a watch) 1-3 x week depending on how you feel.
Once you've built up to this new peak mileage, you should definitely be careful. If you feel something coming on either sickness- or injury-wise, drop the both the intensity and the mileage. Also, you shouldn't be hitting your peak mileage every week. A four-week cycle might go something like:
Week 1) 70 mpw w/ a threshold mile workout, a 30-40 minute tempo run, and a 14 mile long run
Week 2) 60 mpw w/ a 5-8 mile cutdown from 90s/mile slower than 5k pace to threshold, 12-20 x 400 @ 5k pace w/ equal recovery, a 20 minute continuous threshold, and a 13-mile long run
Week 3) 70 mpw w/ a 30-40 minute tempo, a long hill workout, and a 14 mile long run
Week 4) 50 mpw w/ a 12-mile long run, a 20-30 minute tempo run, and a 3k-10k race (this doesn't need to be done every cycle, and can be replaced by a hill workout, a a workout w/ 20 total minutes of threshold [like 4 x 5 minutes], or some shorter 5k-paced stuff like the 400s workout again)