It seems to me like the primary benefit of typical EA donors (say, most GWWC members, or anyone giving less than $100,000/year, i.e. the vast majority of us) giving effectively comes from the signaling effects of this behavior on helping to promote a culture of effective giving and effective altruism.
It still seems very worthwhile for typical EA donors like me to donate, since the direct value of my donations is still substantial and there's potentially this even greater signaling benefit on top of that.
That said, as Ben Todd summarizes in his answer, most EAs (i.e. everyone not in the reference class of people who have a nontrivial potential to become very wealthy EA donors) can probably do even more good through various kinds of work that help deploy the large amount of EA funding that already exists better and faster than they can through their modest donations.
Given that, I wouldn't want to encourage a small donor to donate a modest amount at the expense of them putting less time/effort/attention into shifting into a very valuable direct work career that helps deploy existing EA funds faster/better. But, if donating some percentage of a person's typical income helps keep them engaged with EA and thinking about important questions related to how we can all do the most good, then it definitely seems worth doing to me.
If anyone thinks I'm wrong about this, please let me know!
Can you say a bit more about your reasons for believing that the current funding overhang will be temporary?
E.g. Sam Bankman-Fried's net worth is growing very rapidly (Forbes now puts it at $26.5bn), so there seems to be some reason to believe that the funding overhang is growing at present.
Also, even if we do find new large opportunities to spend money, I think it's important to pay attention to the size of small donors' contributions relative to that of larger donors. Even if the funding overhang shrinks, they are going to be relatively less important, if the greater the total amount of EA funds is substantially larger than it previously was.