Increasing the depth, or 'thickness' of a clear coat, gloss or matt, is self-defeating. Yes, you may end up with a smooth, even surface - eventually. But, this will be at the at the cost of loss of surface detail, and severley diffused paintwork, which will not only look different in shade and 'sharpness', but will also become darker the more coats of clear are applied.It can aslo have the effect of distorting the percieved shape of a model.
The raised detail is not a problem - it was, until relatively recently, the only way mould manufacturers could reproduce panel lines, joints, control surfaces etc, and the now common engraved surface detail is still, to me anyway, a luxury!
Using decal solutions will allow the decals to conform to much worse undulations than a triflingly small. raised panel line detail, and is much better than trying to achieve something which is, to be blunt, a total waste of effort, time and materials.
The only reason for the gloss, as you are probably aware, is to prevent silvering of decals, either from trapped air, or decal-film diffusion, although a gloss clear coat aslo has the effect of 'sharpening' a paint finish, to an extent.
Having stated all the above, if you want a really smooth, even surface, without the 'hassle' of using clear coats, and which will allow raised and engraved detail to still be visible, then use gloss paints, finishing with a matt clear coat if required.
In enamels, Xtracolour formulated a superb gloss range just to cope with this problem, and these are availablke in a full range of military and civilian colours.