Snapmaker does sales somewhat regularly, so personally I’d not hasten things. If the noise is a problem depends on your exact situation and your personal sensitivity. I guess the machine can keep you awake even through a door, but this may depend on your exact situation - I’d first try it out before spending another several hundred bucks. If you do CNC milling, noise of the mill/bit will be the main issue anyhow. IMHO the new modules have even the disadvantage of less torque, which with milling might be an issue (although admittedly I yet have not seen any reports of the new modules being too weak). The new modules can be driven faster, but the + in speed is a bit disappointing IMHO. It still does not make the Snapmaker a fast printer.
The old printhead’s main issue is part cooling, which is really bad. However, it is relatively easy and cheap to attach an external cooling fan: 3DP Part Cooling Fan 5015 Replacement. The new version is better, but apparently still not good (according to several reports), so you might end up adding an additional fan anyhow, even with the new version. The dual printing head remains to be seen: I know of noone having it yet, so reports are missing. From the blog/adverts I have hopes that it is better, and I ordered it.
The PSU seems to be considerably quieter, but if you are willing to tinker, even the old one can be made quieter with a better fan.Aside from the noise and a bit of (useless) LED magic there is no reason to replace the PSU.
I refrained from buying the updates, despite having received the 50% off coupon (which you as a Kickstarter backer also should have). For me noise is not an issue, having the machine in my basement. I prefer the stronger torque, and I hate to waste perfectly working modules without need. On the contrary, I used the opportunity to buy used old modules from someone who updated to have spares and perhaps to play around a bit and build a more robust CNC mill with two modules in the X axis, attaching a much stronger spindle then.
I’d like to have the rotary module, which I think is a cool addition, but for me the use cases are so rare I cannot justify the price, even at a discount. In one of the sales I got myself the stop button, which puts my mind at ease, but a simple extension cord with a switch will achieve the same, so the ROI is debatable.
The air purifier did not even trigger my interest - I can easily vent to the outside, and honestly both the purifier as well as the cartridges look rather expensive to me, but to be fair, I never researched comparable solutions.