Glazing a light wood like maple to look like a dark wood is going to impart cloudiness and or uneven color. Glazing doesn't harden, it dries a little, but mostly keeps a surface that can be moved around. Therefore, after glazing, I like to spray a finish on instead of brush or apply by hand.

To answer your questions, first, it depends how much glazing is left on the surface if it looks cloudy. I like to use glazing to antique a piece, not as a stain. When I glaze I want the color uneven. I want corners, edges to look darker, like they've seen more wear. If you're using glaze as a stain, its difficult to apply over a finished surface as a stain without it looking as you describe. Dry brushing helps I've found.
Durability of glazed cabinets is the same as any other. The glaze offers no protection, its your finish, lacquer, poly, varnish, whatever that provides the durability. Alder is a great wood and is the cherry of the west. A great wood that can be made to look like many others. I have no idea if it will match. Glazing maple cabinets to look like cherry, using Alder to look like glazed maple cherry cabinets... The problem you're going to have is he is applying stain to new wood, how the Alder takes the stain you'll only know once its applied. After the new cabinets are to your liking, then I'd mix the glaze on a maple finished sample (similar to your current cabinets) to match the Alder new ones.

Just remember, glazing is just another form of antiquing, and you will get some variation in the finish because of the manual nature of both the glazing process and the mixing of the glaze itself.

Here is a link that might be useful: Glazing kitchen cabinets info

Glazing is just a way to make it look dirty.

I'm not sure about that... Glazing is one of my regular techniques. More things leave my shop glazed than not. While one technique is to, as it's known, "Dirty up," there are other applications:
* Increase richness and depth
* Accent molding, carving, grain and distress marks
* Faux graining
* Faux aging
* Blend dissimilar colors
* Alter hue or color (add or neutralize colors)
* Subdue stain color
* Control splotching

Most often, I employ them to 'tweak' colors to get a good color match when I'm either trying to match something or I'm only stripping part of a piece or part of a set.

Kitchen cabinets made in the last 15 or so years are candidates for having conversion or 2K finishes on them. These are tough-wearing, but most, if not all, finishes (including themselves outside a very right "recoat window") have a very difficult time adhering to them. If you have one of these finishes, post-factory glazing may not be an option.