A whole bottle of Iron X even on a Highlander is a lot of Iron X. It's not a bad thing, but I think with experience you'll learn to use less product. I always do a horizontal panel first to determine how contaminated the vehicle really is. Horizontal panels like the hood, roof and trunk usually get the most contamination. Try just the hood next time with large sweeping motions while you're spraying. If you don't notice a lot of "bleeding", then I would save the Iron X for another day or use it as a wheel cleaner and proceed with claying. Of course, it doesn't hurt to use the Iron X, but if you're trying to save money and product it can be saved for another day.
I've never rubbed Iron X in, but I could see using an applicator pad or even spreading Iron X by hand with nitrile gloves on as being really effective and saving even more product. Since only the thin layer of Iron X that's making contact with the paint is actually doing anything, spreading it around would allow more of the Iron X to make contact with the paint. For example if you had a hood with heavy contamination, I would bet 2 light coats of Iron X spread around would be just as effective as 2 heavy coats of Iron X while using less product.