What is “essential” to your monitoring environment? (hey, this *is* a monitoring blog. I could certainly ask that about your kitchen, but that would be a completely different discussion)
Seriously – if your budget was infinite, you could have all the tools running on giant systems with all the disk in the world. But it (the budget) isn’t (infinite) and you don’t (have all the toys).
So start from the other end. What could you absolutely positively not live without? Is ping and a DOS batch file enough? A rock-solid SNMP trap listener? Is it a deal-breaker if you don’t have agents running local commands on each server?
Draw a line. Come up with reasons. Know where you stand.