Can't comment on the in ear monitors - I've never used them, although my band has considered them before.
With the bad mixes on stage, I reckon that as long as you're not being drowned out by the screams of your rabid fans, if you can't hear anything on stage it might actually be because someone (with an amp) is playing very loud on stage and drowning out you and the other band members that you need to hear. Listen to see if you can work out exactly who/what you can hear. I think if you really can't hear your own kick drum then something is pretty loud!
Does your band really need to have that much volume coming off the stage or could it be turned down a bit on stage and fed through the PA? This depends on the style of music and how you guys want to present yourself, but bands I've been in usually find that if you actually trust the sound guy a little bit he will usually give you a pretty good mix out the front. If he's working with poor gear or he's in a rush that's going to be his priority - not getting your monitors set up perfect. So you can ease off the volume on stage and let him get them mix right. That's his job and he (supposedly) does it for 3 bands every night in that same venue with that same gear.
There are some bad sound guys out there, but if you're having the same problem all the time chances are there's something you can control too.
Also make sure that when you're soundchecking you actually play at the volume you are going to play live. If you sound check like you're playing in your living room and then come out with adrenalin pulsing, crank your amps and play twice as loud things are not going to be right. Give the sound guy the benefit of an "honest" sound check.
On the night if you find yourself in a real bad situation the worst thing to do is rage against the sound guy in your head. You've got to stay calm and positive and control the gig. Negative thoughts about anything will affect your playing.
I would also ease up on the washy cymbal parts, simplify certain parts (just go for the BIG hits, that's what they notice anyway!), and smack the back beat loud to keep the band together.
Cheers, Good luck