Re: It's a long way to the chemist, etc...
Super-advanced aliens are using comms tech so advanced that even though their signals (and space stations / ships) are all around us but we can't detect them
Super-advanced? You mean the average modern USAlian, I think.
What would be detectable from many light-years out is radio broadcasts using 20th century modulation (AM, FM, SSB etc.), and radar-illumination transmitters. We're already moving away from these. I anticipate that by 2100 broadcast radio will be extinct. Civilian radar may have gone the same way (replaced by GPS and active location transmision by planes to ground control through an evolved internet). That leaves defence radar, and maybe military stealth technology will have rendered that obsolete as well. (Also taking an only slightly longer view of things, either world peace will render defence radar obsolete, or world war will render advanced civilisation obsolete).
Cellphones, wifi etc. are (or rather, will be) undetectable from many light-years out. An efficiently coded signal is almost indistinguishable from noise, absent knowledge of the coding. Also the radio power per channel is at most two watts (usually more like two milliwatts) rather than the megawatts which Radios Moscow and America used to blast out. As the cells get smaller, so do the wattages.
Assuming technology develops along similar lines elsewhere, the era of accidental long-range interstellar signalling probably lasts for about a century whether its civilisation survives for aeons or not. Which is as good a reason as any why we haven't spotted (another) one yet.