Queen common wasps (Vespula vulgaris) are very active at the moment. After emerging from their overwintering sites, the queens must build their paper nests, lay eggs and raise the first batch of larvae. They also need to feed themselves. Wasps do not have long tongues and need accessible nectar or other sugary sources. The wasps in my garden love the spurge for that very reason (above), and later in the season they feed on Fennel and Ivy flowers, which have easy reach nectar. They act as pollinators like bees and hoverflies.
They also like ripe fruit and sap from tree trunks.
The hunting wasps do later in the season (insects, spiders or scavenged meat from sandwiches or carcasses) is not for the adult wasps to eat but for their carnivorous larvae, which will feed on chewed up meat or insects and exude a sugary substance for the adult wasps.
I do not really know what wasps are up to in my cherry tree (photos above from 28th and 29th of march). They do not visit the flowers but the emerging leaf buds. Are they searching for the nectaries? I doubt it. The photos show they seem interested in the bud covering leaflets. I'd be interested to hear if you know what wasps are getting out of it.