I have trained and raced well on both high mileage and low...but when I succeeded off the lower mileage I had one long slow run during the summer (which seem to set it up).
As far as getting injured off high mileage - I certainly understand your concern. I would say - make sure your diet is good - many injuries are diet related (drink milk, eat fruits and veggies)...maybe even have your blood tested now just to see if you have any issues (low iron etc.). If everything looks good - here is what I would suggest.
Any time you make changes to training they should be gradual. Most really good runners (and you are definitely in that class) have a difficult time running slow because you are so efficient at faster paced running. The slow running seems very pointless...when I was in college I ran with the CC National champ on our team - he ran some of the slowest recovery days ever - us younger guys did not run with him because he was so slow...but what he was doing was fat burning. This is what I would recommend you try. As I said above my summer had 1 long, but slow run that set up my whole best season ever on lower mileage. My friends would go 7:30 pace for 14 miles - I hated that run...to me it was so slow all I could think about was food, and wanting to stop = which is when you know your are doing the run right...the pace is so much slower than you are used to it forces your body to switch from glycogen burning to fat burning. For you - I would say try to go 8:00+ pace - go for time in the beginning...like for 1 hour = that will only get you 7.5 miles but that is enough for the first few attempts at this.
2) after you learn to go slower on your long run...your easy days need to be done at about this same pace - to help you recovery + to burn fat. The cross-training you do is okay (I have done cycling, rowing, swimming) but nothing is like running...these other activities can be good to reduce injuries, stress, and burnout...but they don't need to be done too hard...but truthfully, you want to be a better runner - you need to run. The very best runners run twice a day. Try doing one or two double per week - even if you only go 2 miles...when I first added doubles within the last year I would just do 4 miles...the doubling is the benefit, not the distance.
3) change all you hard intervals days to tempo runs...these are the most important workout you can do to get better (especially if you are doing the one long, slow run)...but these need to be done right. Do not race them...Do not worry about the overall time. the goal is simply to run miles at an efficient pace = what is that pace?
your body and brain are the best ways to determine the tempo pace, not some form chart. When your breathing starts to get heavy, you are going too fast - slow down. WHen you brain tells you, you are going to have trouble holding this pace for the distance you were shooting for - your are going too fast - slow down. I think the range for most runners on the tempo is actually quite large. If I can race at 5:00 pace - then my tempo pace of efficiency might be anywhere from 5:20-5:50 (most of us mistaken try to run the faster of the range when we should start at the higher end and gradually come down during the tempo)...it is also fine to kick it in at the last 1/2 mile or so...but don't get concerned about your overall time and try to compare to your last tempo...weather changes, how you feel changes, etc. As long as your are putting in the work (controlled work) at the proper feels right pace, you will improve. Also don't be afraid the vary the tempo pace - one day I may run most of my tempo at 5:50 but go longer (like 8-10 miles) another time 5-6 miles at 5:25-5:35).
you are already very fast...so you cannot have been doing too much wrong, but if you want to tweek it - only gradually increase your mileage, but mostly decrease your intensity now (during the summer) so when you come back to intervals in the fall they will be easier and faster. We all want to interval ourselves into great shape, but the real work toward improving fitness and making those leaps in racing happen during the off-season where we build our base (slower paced running, doubles, and some tempo). Think of intervals as sweets in your diet - they are great and add a lot, but use them sparingly..the bulk of you running meal should be slower volume. I coaches a high school state champ with very similar times to yours and she also trained the way you do...the idea of running slower to get faster was a hard sell. It took me years and years of running myself to accept it. It does work. All training does not have to be hard or fast.