I think German prestige on the continent is more important to the Kaiser than prestige overseas. I doubt a few colonies would be enough for him to return A-L to France.
France and Britain are colonial powerhouses even before German and Italian unification, why should they give up their colonies to such young countries? No, I think the only way Germany and Italy can gain anymore is through a first-in-first-served method. If they were richer, more prepared and faster then they might be able to grab a few slices more (I've always liked the idea of an Italian colony on the Gold Coast, mind you).
The problem with King Leo was that Germany, France and Britain all wanted the Congo (some more than others, probably), but neither France nor Britain wanted to see it in German hands. Leo was a good compromise (which later turned to shit).
Furthermore it appears that at the time German Imperialists*, actually were more interested in the Philippines, Formosa and (East) Timor (and at a later date the protectorate of Morocco); although any change for more African Colonies, like OTL Congo Free State, probably wouldn't be refused.
IIRC Italy wanted Tunisia, but any change to increase 'their place under the sun' would be welcomed (for instance OTL Congo Free State).
If France wants to convice Germany to sell them Alsace Lorraine in return for colonies, then France would have to give a lot of colonies, for instance French Indochina,( perhaps Madagascar, perhaps French Polynesia,) the protectorate Morocco, parts of French West Africa and parts of French Equatorial Africa. Any price reasonable for Germany most likely would have seemed ridiculous for France and would also have caused objections from other colonial powers like the United Kingdom. And much more important it should not be forgotten, that at the time it was the age of nationalism, Alsace Lorraine was considered a part of the German nation by Germans, so selling them could cause internal opposition of nationalists.
Otherwise a likely outcome of the conference would be minor border alterations, slightly different from the OTL.
*= Bismarck wasn't (yet) very enthusiastic about colonies, but obviously there already was a more pro colonial movement