I often wonder the same. You sound well placed because you have some older compost which, I suspect, has plenty of goodness, but it probably needs sieving which is easiest if it is more dry than wet. Not too fine a sieve, to remove twigs, stones etc; lumps of compost are not a problem i.e. it does not need to be super fine.
You can add some nutrients but take a look at these photos to have an idea of the enduring quality of homemade compost, which is the pot at back right. These are lettuce plants which I potted last July into "Everbloom" bottom left, West Riding module compost bottom right, cow manure top left and my own compost top right.
JULY 
AUGUST
SEPTEMBER
I was impressed by the different qualities of each compost – West Riding for the fast growth initially, then an abundance from the manure, and most staying power from the homemade compost. There were no extra nutrients added and some leaves were picked after each photo to keep plants of a manageable size, picking to the same number remaining on each.
The "Everbloom" as labelled ‘organic farmyard manure’ but looked and behaved like green waste compost.