Firstly, thanks to both Homer and Gaminari for your responses.
I can't tell you how many documents we've been sifting through in utter desperation. These have included Gib immigration legislation available via the UNHCR site, European Council documents on the rights of EEA Nationals and their family members to move/reside freely in member states, as well as any other travel/tourist sites such as VT.
I had also seen the gib.gov.uk site's FAQs which Gamiari points out, and had referenced this when talking to the people at the London Gibraltar office. They freely admitted that yes, it's a catch-22 because they are also fully aware that Gibraltar will not recognise these documents so, as Gaminari says, how can anyone get a visa in such a document. Just to clarify, I am aware that we must have a visa, and fully prepared to go through that process, as my wife has already done so for 2 previous Gib visas.
My wife has had 6 previous UK visas, 2 of them being long term (1yr+) which may be used for Gib entry, 1 EEA family permit, and 2 Gibraltar visas. We're really getting very intimate with this whole visa app. process, so I have no doubt that, given the opportunity, we could submit a solid application. I can support financially, and I had also tried to allay immigrations fears by stating that we have private health insurance in Gib, so she would be no drain on public funds. Unfortunately it appears that this very opportunity is what i'm not going to get.
As a side issue, I had also recently asked immigration if I may apply for a Gibraltar visa for my mother-in-law. My wife's father died very suddenly and I hoped that, under the circumstances, they may look sympathetically on a request for my wife's mother to visit us during this difficult time. My catch-22 in that case was that I need a 6 month rental agreement in order to register with civil status, but I am in company accommodation for the first 3 months. Until I am registered I can't apply for/sponsor a visa. Long and short ...at this time I can request a Gib visa from any country other than Gib. Aaaah!
In both Luxembourg, where we had lived before, the process is far more straightforward. You sign what is named a "prise en charge" which obliges me to cover any costs which the state may endure during a visit.
As a last point, when we asked a Gib policeman on the border, he recognised the travel document which we were referring to and said that this was no problem for entry into Gibraltar. This added to my surprise when immigration put up the brick wall.
If this was the Belgian authorities saying no, I would likely lodge a complaint at the British Embassy in Brussels. However, in this case it appears that I have nowhere to escalate this to. Moreover, although I have raised this with the Foreign and Commonwealth Office, I fear that when all is said and done, Gibraltar has the final say, regardless of any UN or EU legislation on such cases.
As you can see, we really have looked into this in detail, but feel absolutely desperate.
We had received very helpful responses from Homer on this forum before, so we turned to VT.
I have no clue where we can go from here, but it's difficult to look forward to Christmas and the New Year with this hanging over our heads....