Howard - whenever you get a chance, I would revisit brettus' post #55. Rather than getting into an IC in two credit spreads, you can get in in a pair of risk reversals.
The advantage is that you pay less for your long options. The disadvantage is that you are carrying directional risk until the IC is completed. Being directional, it is a very different approach to entry by credit spreads. But the idea is to buy your long options very cheap and that advantage may allow you to scale down for a similar expectation.
I realise that you aren't keen on taking a directional view, but maybe you can combine this method of entry with your probability of touch.
I also agree with sj (post 66) - Taleb's dynamic hedging is a good read (if a little cryptic at times) and is a bit unusual in looking at a book of options (rather than one). On practical, empirical vol models I suggest looking at Euan Sinclair's books.