Using pure O2 is a great way to blow up your engine REALLY fast plus there is no way you could carry enough of it to last more than a minute or two in the mountains. Nitrous Oxide is commonly used because it turns to a liquid under high pressure so a lot more can be stored in the same bottle space. Even still, a 30lb bottle will only last 2-5 minutes. A 20CF bottle flowing enough to make a noticeable power difference wouldn't even last 1 minute.

Your "maintenance hassles" are imaginary. Caring for a turbo engine is no different than a non-turbo engine. Maybe once every year or two you should check the shaft play and thats all it takes.

Highway 17 has a maximum of 5.8% grade around Cumbres Pass and an average of 4%. Even a 240D should be able to maintain 30-40mph up that without a problem. If you had to pull up to the pass in first gear you have some performance issues that need to be taken care of before considering power adders. "Cheaply rebuilt engine" may be part of the problem.

What is your current 0-60 time?