Up Next... Power Liine Conditioners, DACs and DSPs

I have finally reached the end of my component search and have the following: McIntosh MA650 integrated amp, Arcam CD-92 cdp, an old Tandberg 3011A tuner,and Soliloquy 5.0 speakers (coming soon -- I have Tannoy D500s for the moment -- downsizing to appease the wife). Very happy with this set up. But my audiophile bug hasn't gone away and I've lately been reading about power line conditioners, digital/analogue converters and upsamplers. Sounds like more fun. Any thoughts on whether these are worth their salt? Will they really add something pleasurable? Are we starting to spend a lot here for just a little benefit?

Thanks,
AT