I used to have a 228i, the lightest of the 2 series, ~3200 lbs. A blast to drive already, a more comfortable daily driver with more amenities, better sound proof and acoustic, better interior air quality, better all-around visibility, higher off the ground, easier to daily drive. Actually faster on the straight line and a handful in the twisties compared to the BRZ.
I've ridden in the M2 Competition; it's along the same line with firmer ride, better performance. Still balanced well, but a heavier car.
Then there's the BRZ... ~2800 lbs. Not as polished inside, loud, rough, it's down a level in comfort and amenities... but awesome driving position. Need a bit more HP, but otherwise easy to drive at full throttle. Need to be at higher RPM to have fun, like how Japanese hot hatch/sub-compact from the 90s... which is how they have the Jackal/Mr. Hyde personalities.
I don't think you need a replacement for any cars. You just want something that feel different, a new drug to get excited again.
What about put some work into the BRZ instead?
I have a 2013. Can't do much about the loud interior noise, but the next main complain: cheap-feeling, stiff handling. And like you I don't mind it a bit higher, up to 1cm. I rode in a friend's WRX, love how compliant the suspension is, firm, but no bouncing, just settled. Most suspension upgrade will lower the car a bit, but this can be offset by the bigger rim-tires.
Second... something my BRZ already have, a turbo, installed by the previous owner, certified too, so no problem registering the car. It's a stage 1, power up by ~60-70 HP, builds up progressively, more on the higher RPM. It'll wiggle, fighting for traction, driven a bit hard in the rain, plenty of power.
Otherwise, for a new car... the 2nd-gen BRZ? The OEM tires they use alone should make it a different car. The 400Z? The Yaris GR? Like what's already suggested above.