Just my two cents:
I own Paramounts, or rather a modified version of the circuit (though I had stock Paramounts), and had the older drivers and converted to the 5670 when I owned stock Paramounts. I have a Kaiju also to compare to. In the past there was a 2A3 Fi X and when compared to the Paramounts 2A3, the Fi was sold though I should have held onto it as a piece of art.
If you're not having an issue with hum, and you're not using it as a headphone amp, you probably won't notice the lowered noise floor with the new amps. I am using my Kaiju as a headphone amp because the noise floor is that low. The new regulator is truly amazing and an improvement when appropriate. As PB stated, the bass is better in the new circuit due to the improved iron. You can add the balanced output (I think this is the correct term?) to your current Paramounts. DocB wrote about it in a thread years ago and it takes all of four resistors to do it. This comes standard with the Kaiju.
2A3's should be tried but for me, it passed quickly. The 300B is special and adds a little something you just can't get with 2A3's. DocB called it Technicolor and I agree with that, it's close to magic and makes listening to music more enjoyable for me.
Try 2A3's and 45's and 71A's. All of these are different and everyone has their favorite flavor. I personally don't care for 2A3's or 45's. My system is 300B's and 71A's. It's an easy swap on your Paramounts to convert to 2A3's. If you like the 2A3's, then the Monamour will be an improvement over your Paramounts in the way PB described.
Plus, new amps just make you happy and who doesn't want to be happy
