Luton town centre is awful and there is nothing for tourists it is true but you haven’t booked an air bnb for a week to explore it, it is serving a purpose and can do that perfectly well.
You are staying right next to Luton Hoo and Stockwood Park which are lovely and a short uber ride away from plenty of lovely pubs and shops in Harpenden and surrounding villages.
It is a perfectly fine option to spend a weekend for your purposes, you have booked an out of town hotel as accommodation for a concert and there is more than enough walking, sunbathing (if weather continues as expected), eating, drinking or mooching on the couple of options I have suggested above to fill the time you need to around it pleasantly.
Make the best of the good parts around you, like the hundreds of thousands of normal people who live there and ignore the town centre if you choose, it is grim it’s true but there is no need to spend any time there.
Don’t be put off by people who have the privilege of not being born into an area like Luton and in my experience, are deeply uncomfortable when they see any deprivation therefore are fearful of it and this projects as judgment but in reality they know nothing about the wider town or community.
You’ll have a great time if you make a plan with the many good suggestions given and reserve your judgement.
Please come back and let us know how you get on :)