It will be more expensive unless you shop very carefully. Some things are similar in price, but some things are way more expensive - eg fruit and veg, meat, fish, cheese.
Whether or not the things are better quality/nicer is up for debate, only you can decide whether it's worth it to you. I've used these vouchers only to find that buying a few more expensive things has wiped out the savings, making the exercise pointless. But sometimes you can take advantage of some good offers and try some new things, and get a bit of a discount on the way.
Definitely take advantage of the free coffee and paper if you have a MyWaitrose card, and thanks for the tip about the free things counting towards the spend bonkers I didn't know that.
I threw my last set of vouchers away because I used to get £8 off £40 but the latest ones were £10 off £60 but I did use them in the past to build up a nice gin collection, but I've put myself on a bit of a shopping ban on this front this year, as I have quite a lot in stock. I'd buy a couple of bottles of nicer gin on offer and a few other bits to make it to £40, sometimes getting one of the lovely but expensive sushi sets from the fresh counter, arguing that it was 'free' because of the voucher.