Brilliant stuff you folk. Hi there Trevor (nice to see you here).
GK and Djaw (David?) have it well sussed out. FATHOM was my choice, but RUMBLE is just as valid.
As for the 'bonus' I like STEAMROLLER. My make way was meant to mean make a street; roughly = make a rough street, do this using "cobblestones" and start with one COBBLESTONE. I've just dealt with a long phone call so someone may have posted while I delayed. Here is my working
1. ANAGRAMS OF EACH OTHER “the public art galleries” and “i bet large picture halls”
2. trim = snip; doggie = (diminutive suggests) pet; trophy at last = y; SNIPPETY = trivial (Chambers def).
3. shopping centres = malls; alien = ET; mall(et)s = MALLETS = beetles (beetle = heavy wooden mallet: Chambers)
4. It’s “in” there! Do = party =SHINDIG
5. (double) get to the bottom of = FATHOM = sound.
RUMBLE would be quite acceptable.
6. (cryptic) COBBLESTONE