The self adhesive pads on rubber feet 'dry out' over time in normal living conditions and eventually lose adhesion. Blu tack / white tack / black tack etc. also dries out and goes hard. However, it tends to keep its adhesive properties, getting harder in my experience. However, with blu tack the speakers do move out of position over time (vibration from the cabinets). I have my speakers on the same sand filled spiked stands I purchased too many years ago to mention, and they are stuck down with blu tack. I check them every 12 months or so and realign them.
As far as ridiculously priced iso platforms are concerned, not worth it in my opinion when you can do an admirable job yourself without much effort and much less money. Isolating the CD player does make a difference, and on mine it sounds leaner, cleaner, and less harsh. It's not a difference of night and day but it is nonetheless noticeable...well, except during the day when everything sounds worse.
In 1985 (when dinosaurs ruled the earth) I purchased a spiked (the feet, and top shelf are spiked; bottom shelf on corner brackets) metal framed Target turntable table (well two). The shelves were made of fibreboard material and covered in black coloured wood effect vinyl. Ghastly really. Anyhoo, instead of ditching them when I ditched the deck, I renovated one of them to take the CD player and Mission amps (amps on bottom TEAC player on top). It was relatively inexpesive and easy. The original shelves were discarded, and in their place some very nice green composite marble plinths I had cut and polished at a local marble suppliers. Two offcuts all finished cost me £30. I bought 2 green smoke 10mm pieces of safety glass from a local supplier, again all cut and edges finished nicely. £12 (it was a while ago). And then a pack of self adhesive rubber feet from Maplins. So, bottom shelf has blu tack on the corner brackets with marble shelf on top and then glass shelf on top of that with the rubber feet in each corner. Amps on top. To marble shelf sits direfctly on spikes, and then the glass layer on top (same as bottom) and CD player on top. Looks amazing, makes the sound much better, especially on floorboards, and it's been like that for a long time now. Disadvantage is that dust will settle under the glass layer, and you will end up cleaning it frequently. Oh, and you won't be able to just pick the table up and move it with everything on unless you have a strong back. It ways a ton!