Yep, dynos are tuning tools. I dunno if I'd say ETs are pointless. I'd say all 3 individual measurements are pointless when stated on their own. Eg, no point having a 140mph TS if the best ET you can get is mid 11 when its capable of a low 10.
First time at the track I ran 14.3@98mph with a 60' of 2.4. Best 60' on the day was 2.3. Only mod was a cat back zorst. I installed a K&N panel and made 126rwkw on BMT's dyno.
I then added a few bits'n'pieces and made 140rwkw then ran a 13.8@101mph with a 60' of 2.2 on almost unroadworthy 205 tyres. From this visit to the track I learnt that TYRES are the best mod anyone can invest in coz my 60' times were almost unaffected and now wheelspin is an issue in second gear. Mods were: bleeder @ ~10psi, full exhaust (crappy cat tho), stock airbox with K&N panel filter.
I've since upped the boost to 13psi and had a chipped ecu put in. It made 153rwkw. Just waiting for a set of wheels to arrive with new tyres and I'm aiming for a low 13 ET. To achieve this I'll need a sub 2s 60' and maybe a few more mph. I've personally spent just over $1K on mods. I'll be spending more than that on tyres alone.