IMac G5 no Bluetooth on waking from Sleep

Question

I have an iMac G5 2 Ghz model with a wireless Mighty Mouse and Apple wireless keyboard and have recently been encountering a problem with the bluetooth connections to them on waking form sleep. Although I have searched and found threads detailing similar issues to mine, they have not been exactly the same hence my starting a new topic.
The iMac works perfectly and I can put it to sleep just fine. Later on I can tap a key or hit a mouse button and the machine wakes up. However from that point both the keyboard and mouse are unresponsive, I will get the screen pop-up message telling me that the keyboard and mouse are disconnected, the bluetooth icon in the menu bar is crossed out but the machine itself has not crashed, the clock continues to click up, I have an animated desktop background which continues to play and if I plug a standard USB mouse in, that works.
If I leave it alone (literally for five or ten minutes), then nine times out of ten, the mouse and keyboard will suddenly start working, disconnect again for a few seconds, reconnect and then work perfectly for the rest of the day as long as the iMac doesn't sleep. Sometimes the bluetooth system simply doesn't come back up even after twenty minutes or so and I am forced to hard reset the machine an reboot. From a restart, the system always works perfectly.
What I don't understand is if the bluetooth system is loosing connection when asleep, how comes a tap on the mouse will wake it up ok and then it disconnects?
So far I've reset the PRAM and Power Management systems, trashed the bluetooth preference files and restarted, and run a permissions check. These seem to make it better for a while but the problem comes back. It doesn't seem like a hardware problem in that it all works perfectly while kept awake but I'd be grateful if anyone has any suggestions as to what I can try next or look for.
Many thanks in advance.

Answer 1

OK obviously tempted fate by posting, the bluetooth problem has returned!
While awake both the keyboard and mouse connections are rock-solid, on startup, both connect instantly it's just waking from sleep that's the issue.
I had the problem just a few minutes ago, the Mac had been asleep for about 30 minutes, I tapped the mouse and it woke up, I could even move the mouse pointer around for a few seconds and then it suddenly froze. The Connection Lost message (for the mouse not the keyboard) appeared on the screen and the bluetooth icon in the menu bar changed to the 'no connection' sign. If I flip the mouse over the little green led doesn't come on.
After about ten seconds the bluetooth icon changed to normal and the mouse worked-for about two seconds then the whole cycle repeated. This happened three times, the mouse worked for a few seconds, the connection dropped and I had to wait about twenty seconds for it to come back to life on its' own. I tried the volume up and down on the BT keyboard but that wasn't working either. On the third time of dropping, the bluetooth assistant fired up telling me that there was no keyboard attached, just as the mouse resumed working on it's own. It searched for a keyboard, told me that it couldn't find one and then immediately told me that a keyboard was attached and no further action is required.
And from that point on both have worked perfectly. If it was just the mouse or the keyboard, I'd suspect that was the problem but I find it hard to credit that both would fail at the same time.
Well I'm now officially stumped. Surely it's inconceivable that a failing BT module would not work on waking but be perfect all the rest of the time?
Any ideas or suggestions would be gratefully received.