It is possible to achieve huge values for the Purcell factor of the whispering gallery resonator composed as a raspberry cluster (a spherical metamaterial shell of a submicron dielectic core). The metashell is formed by mutually touching plasmonic nanospheres adsorbed on the core of diameter 150-1500 nm. Nanospheres of diameter 8-11 nm are ohmically isolated from one another by a 2-3 nm thick dielectric covering or by an encapsulation. The combination of the plasmon resonance of nanospheres with the whispering gallery resonance of the whole metashell turns out to be multiplicative for the local field enhancement. This effect opens the way to new schemes of SERS.