We were in a similar situation to you and moved almost 2 years ago from a 1970’s link detached 3 bed house with a huge drive and large garden to a 4 bed 3 storey townhouse with only 1 parking space. Newer but not an actual new build.
Our situation was slightly more complex in that due to financial difficulties in the past we had ended up on an interest only mortgage but due to how long we had lived in the house had built up sizable equity so selling helped us to free up that equity, put a large deposit on new house and change mortgage to repayment.
our main motivators were that old house was very cold and draughty, likely needed new roof and windows, the garage was damp and to use the space we would have have to knock the garage down and start again but would have cost £££.
we needed more space as have 2 teens. The smallest bedroom was a box room and not big enough to study in.
we only had 1 bathroom/toilet and 4 of us in the house so we ideally wanted more bathrooms.
We couldn’t afford a large 4 bed detached with lots of parking but what we have now is big bedrooms for everyone and more bathroom space. Yes the parking is worse and actually smaller garden hasn’t bothered me.
what are you main motivators for wanting to move? If I could have stayed where we were but extended to get what we needed then I probably would have stayed but our reasons for moving were very specific.
definitely write a list of pros and cons. Not all new builds are awful but some seem to be less well constructed than others. Do you like the new area better or would that feel like a compromise? Do you have good neighbours now? Bear in mind if you move you might get amazing new neighbours but they could also be awful.
added bonuses have been lower elec/gas as house is better insulated and much warmer, we’ve moved to a different part of town, kids closer to school and work and our commute is much smaller plus the other side of town which used to be a nice place to live is getting a huge new build development which will cause lots of traffic and congestion issues
good luck whatever you decide to do