Replacing my tweeters a good idea?

Do not replace the tweeters. A better tweeter won't necessarily give better performance; loudspeakers are systems. You might get a few things better with the new tweeter, but you'll probably sacrifice a whole lot of other things because that tweeter isn't being used in an optimized condition (crossover freq. may be off, etc.)

Wire a resistor on the tweeter leg to tame the irritability. May have a resistor now, but I have found most cheap speakers have REALLY simple crossovers(bereft of components). A good, wire wound from a company like Ohmite(better than what's in 99% of the speakers) will not degrade the sound(in fact, I have found they get rid of much of the brightness and glare - even when the same value as an original is used). The value needed would be from one to three ohms(depending on your current crossover - and how bright the speaker really is). Cost would be about $2(assuming you wire it yourself). If you want to do it temporarily, remove the positive lead, wrap the lead of the resistor into that connection, and use electrical tape to connect the resistor to the cable. Play it for a week or so before you make a conclusion. If you are happy with that, fine. If not, go ahead and buy a Vifa or Seas($15 - $25 each, depending on model - get one of the cheaper ones) tweeter that will hopefully drop right in. You won't need a Dynaudio, a driver is only as good as the crossover behind it(and the crossover in your Infinity won't be the best ever). Use it without the previously installed resistor(unless your speakers came with a resistor - then use the Ohmite). Some may say don't change the tweeter, but at this point, what's the difference? You are unhappy, and will replace them at some point if you continue to feel this way. So why not take the chance? Good luck!

You are obviously not happy with the speakers as they are now, so what have you got to lose by experimenting! Try and get as much information on the specifications of the existing tweeter (there must be some somewhere on the web) and then see if you can match as closely as possible to this with a fabric dome tweeter for starters - as Trelja suggests try SEAS, etc. The specification you will need to look at closely is the impedence, resonant frequency, crossover frequency, etc. Have fun! Richard, vantageaudio.com

Wire a resistor to the tweeter leg? I am new to modifying components - could you be more specific? The tweeter is an infintity EMIT-R type. Thanks for the help!

Just splice the resistor into one of the leads to the tweeter; positive or negative won't matter. You could use an 8 ohm pot temporarily to get the exact value you like, then buy a fixed resistor of that value. If you still can't get it right I'll sell you my nice pair of 19mm Seas plastic-dome tweeters cheap. (I'm through with speaker building!) Good Luck.