It honestly depends. Do you like the sound you are getting now? Are you getting complaints about how it sounds from listeners? Are you having trouble with the FOH system feeding back at
multiple frequencies?
It can be a tool to use there, given certain situations such as lots of feedback at widely separated frequencies, but for general shaping of the tone, it sounds like you are doing a pretty good job already.
Are you running your 450's off of the outputs of your subwoofer? If not, they may be overlapping in frequency with your sub, and causing a buildup of lows/low mids, that would need EQing to correct.
If you think this is something you should just have, because you see it elsewhere, think twice before purchasing one. Think about how satisfied you are with the results you have now.
-MIkey P
P.S. It sounds like you are already taking an interest in system tuning and alignment, you may want to check out Smaart from
SIA Software for a PC based system to measure your PA. It is an extremely deep program, and understanding it's output may take awhile, but there are plenty here on this forum and in the LAB to help you, as well as training and articles available from Sia's website.