Hours building is where gliding experience can, I believe, come in handy. Having such experience makes you much more attractive to a club who is in need of a tug pilot, if you're a member of a club you can put yourself forward. I've seen a couple of people gain a couple of hundred hours towing before going for their CPL/ME/IR. The only thing is that it isn't "structured" hours building.
Would probably take between £10k-£20k off the cost of a licence which, if you're doing modular, is a fair bit.