FF, I doubt 4,000 students will be prepared to pay "Premiership" price that often. To match Wasps and Saffas ticket income they'll need to have much larger crowds than them as it's not just about the numbers through the door, it the income they generate. On top of that, to have about 25% (very roughly) of your gate, leaving the area every year is a very dodgy business plan.
The students populace is approx 25k, give or take. Add in the folks from Summertown, Botley, Headington, and the Abingdon road area (the more affluent areas) and getting a regular attendance of 4k to 5k isn't out of the realm of possibility at all. I doubt you'd get too many from the Cowley Rd and Iffley road areas, but still, there's a population 50% larger than High Wycombe (157k vs 95k), so equalling Wasps attendance is definitely not out of the question. Add in the local commuter towns such as Kidlington, Abingdon, Didcot, Wantage, Witney, etc, and there's a market that they can exploit, particularly if they get their pricing and marketing right....
You come off at something like J8 of the M40, then go on the A40 on the ring road around Oxford and eventually there are signs to the stadium.
If you're coming up from the Kew/Richmond/Twickenham area, far better to come along the M4. Then you have the option of leaving either at J12, and coming up through the local villages (with more than a few decent pubs along the river) or J13, up the A34, and two stops round the Oxford ring road. I'd only do the M40 if the M4 were closed...