I don't particularly care about lounge access - but SQ is a hassle-free option vs. alternatives. Quite like VN on this route as well.

Check-in experience, customer service, experience on the flight etc., carry-on luggage etc. etc. - SQ will be around a million times better than the LCCs.

Things do go wrong sometimes, and I'd much rather deal with SQ if something happens.

As for Jetstar - the check-in experience in Singapore can be really poor and can take a lot of time (ok, talking of landside here). I've also had to check in my cabin bag before (recall 7kg that time). Flying back from SGN, I would expect 2 desks to be open for check-in and 180 pax in the queue (Jetstar / Scoot). Experience on the A320 is ok, but it's 180 all-Y high-density layout. And hey, if the luggage bins are full, your bag will go into the hold after all.