NTA SL100

It will monitor all the switches but not all the ports on each switch. I generally don't monitor access ports. I only monitor the uplinks and maybe an important interface here and there. Just be selective about what you monitor.

I agree with what Superfly mentioned and I'll throw in my two cents.  The rep probably told you that SL100 would be enough because of this math:

30 EX3300 switches x 2 uplink ports per switch = 60 interfaces

However, hopefully those 30 switches are uplinked into two distribution or core switches, so you would want to monitor the core interfaces connected to those access switches.  So effectively we just doubled the amount of interfaces that we want to monitor. Plus you may want to monitor the management ports on each of those core switches and the cross-connect between them.  So I'm thinking you'd need licensing for 120-125 interfaces, and that's just for the networking.  We haven't even touched on monitoring any server ports, security cameras, etc.  So I agree with you that SL100 would not be enough.