Onstage, pity can be tedious. Self-pity — even more ghastly. Nostalgia, discontent and regret are all feverishly personal — and for an audience there is often a disconnect. Amid generational collisions and a disarmingly heartwarming emotional release, Trinity Repertory Company’s “Vanya and Sonia and Masha and Spike” broaches these themes with enough seriousness to compel viewers. Trinity Rep’s delivery has its fair share of party fouls, but Christopher Durang’s script and Curt Columbus’ direction are robust enough to counterbalance acting imperfection.