I know you didn't want to go there with clipless, but if you're going to provide a reason for not doing so, it needs to make sense. Clipping out while skidding isn't an issue with the right setup, particularly if you use atacs or eggbeaters that actually tighten as you pull up. Yes, worn cleats are still an issue, but as cc700 points out, failure due to wear is an issue with any setup. If you really want the best retention, clipless is the way to go. On the other hand, based on the above post, your bike seems to revolve around a particular style, and you may consider clipless to be out of place. That's at least a consistent reason.

As for straps, I haven't tried the holdfasts, but I did use power grips for a while. Everyone else seems to love them, but I could never get solid enough retention to feel comfy even for skipping. They performed worse than clips and single straps for me.