Ericaceous Compost

I have a container full of used ericaceous compost. It had a Rhododendron Impeditum in it, which has sadly died (my fault, it was under the porch and I forgot to water it).
Normally I just tip used compost onto the garden beds as a mulch, but is it ok to do that with ericaceous? It had been in the pot for 4 or 5 years I think, but has been topped up occasionally.
Also can anyone recommend a dwarf Rhododendron of a similar colour to replace it? I was very fond of it but something a bit di9fferent would be nice.

 

No problem reusing old compost as soil improver as long as there's no sign of vine weevil damage or grubs

 

Thank you @noisette47.

 

Might be worth having a Google for R. Yakushimanum hybrids. Some are dwarfer than others but there are some very pretty colours. Or Japanese Azaleas?

 

I've had a Rhodo yak for about 30yrs, in the ground its still only 4ft tall but I must admit I've not cared for it very well.
I think from memory it was Titian beauty.

 

Thank you @noisette47 and @pete, I decided I wanted one a similar colour so I have ordered Rhododendron Azurika.