I'm jumping with joy!!!

If you want some insurance, in case things go wrong, scan the decals into your computer. Then if they disolve or crack at least you have the image to reprint on new decal sheets.

Thanks again for the advice guys...

It seems, however, that I have hit another minor obstacle. 

I, erm, can't find the kit anywhere! Years of moving house and it isn't in the box labelled "model kits - BE CAREFUL!" 

Hmmm..

I have found my un-started Enterprise C though..so, what do you think: Spacedock diorama...?..(I wonder if I dare do a small aztec pattern...)

Noel

It really depends...Now I remember my old AMT decal from a Romulan Warbird didn't suffer much after 15 or so years gathering dust. Fingers crossed for you..

Other brands (eg Academy), you can use their decals to patch up a leaking nuclear reactor since they are virtually impregnable.  

Noted and thanks! I'll be following that to the letter!

To expand on Potchip's post, If you can get hold of Microscale's Liquid Decal Film, apply this over the decals (after sun-bleaching) before dipping  to ensure against cracking/disintegrating decals. Spraying a clear coat over them may work, but the Microscale stuff definitely will, that's what it's designed for.

If the glue has lost adhesion, a decal setting solution like Gunze's Mr Mark Setter (blue bottle) will help as it contains a mild adhesive and will pull the decals down nicely. Most other decal solutions  are solvent only and do not contain any adhesive.

Good luck and may your decals hold together.  

To be extra extra safe...

You sound happy, just some advice based on own painful experience:

Expose the decal under the sun for a day or 2 - this will reduce any yellowing

Test a small piece (eg the brand/label) in water and ensure it does not explode as if hit by a photon torpedo - which old decals tend to do. If so - tape decal to a flat surface and spray clear over - then cut to shape - this holds the 'film' together. You tape it to a flat surface because as paper absorb moisture it will typically curl, and you don't want your decal to curl from clear and dry curly. Worst case if paint pools, the solvent in the paint may even attack the decal.

Personally I would spray the decal with clear regardless - better safe than sorry.

Glue may be deteriorated over time so you'd might have to wash off the residue (because old glue are not clear) then use decal set as alternative.