The truth is that GA pilots transitting under IFR & in IMC in Class G airspace are highly unlikely to be listening out for gliders on 130.4. In fact I don't know of anyone who routinely does this. In general there are more appropriate frequencies, on which one can obtain either a RIS or FIS, depending on the circumstances.
Our company requires us to obtain such a service so we are always in contact with the local ATC unit. If our track takes us close to an ATZ, the published frequency for that goes on VHF box 2 so we are likely to be already working two frequencies. We are otherwise required to listen out on 121.5.
We are infrequently but very pleasantly surprised to hear glider pilots advising ATC of their presence, which seems a very sound idea, bearing in mind that most gliders don't show up well on radar and don't carry a transponder.
I can understand that a glider pilot flying in very close proximity to others might consider 130.4 the best frequency to use. However, whilst operating in an area where GA aircraft are likely to be transitting, it is in everyones best interest for the glider pilot to consider making contact with the appropriate ATC unit, to enable them to warn other pilots of their presence and allow some sort of co-ordination to take place.
Although CFIT accidents are more common (the ground is EVERYWHERE, so it's not too surprising) a mid-air is often just as fatal to all concerned.