I invested around 70-80k on this event and got top10, but I only participated last 2h and my unit pool is very limited (58lvl now).
I differenciate 2h before event ends, if I can get top10 or not. If not, top200 is ok. It mostly depends on prize range. I guess you have to go at it on a day-to-day basis. No clear cut best way.
For Cassian/Jyn event I went in similarly with top25 results, but I won't do it again. Farming toons is not worth it since they are chromium exclusive so until they implement them in cantina nodes it's pointless to invest. Best way is to pick a optimal prize range and stay stay there.
This tournament netted me 60 Vader ship shards, so it was worth 80k ally points imo.
Buying bronziums seems good if you got some toons to 7* already with vast pools of units. That way you're bound to get at least some usefull ones + you can trade them in shard shop for smth good or gear. On lower levels it's similar to buying chromiums, you might get smth good, but whats the point if you can't progress farming it or dont have money to gear it.
Care to elaborate what you think ?