Why did you choose to have ec2s with postgres rather than using RDS? I've found it saves me a ton of time dealing with upgrades worrying about backups etc to have RDS handle it.
I love RDS, but having maintained complicated Postgres setups before (at my previous employer we had a few dozen Postgres servers for different big clients, all set up with replication to different geographical locations etc. as well as automated log shipping and backups going to a "homegrown" blob store), it's not that much effort.
What you gain is the flexibility to control e.g. which extensions you want to run, and exactly how you want to set it up. How important that is really depends on what you want to do.
Not OP, but I set up a SaaS platform, and I also ran on straight Postgres (RDS wasn't an option, we weren't on AWS). In my experience, after setting up WAL-E to continuously backup to S3 and giving it plenty of extra disk space (for stalled WAL segments), it worked pretty well with no intervention. Restores occasionally took a bit, but they never failed (we managed a couple dozen databases over five years).
If you know what you're doing (important qualifier), I'd imagine cost is a huge factor too. RDS is pretty often a significant % of your AWS bill - how valuable this is, entirely depends on how confident you are doing it yourself.
