We went through the same procedure as you several years ago. We bought a resale Garden Lago week (1st week in July a 2 Bed Standard) and the first time we used it we had a visit from the Rep (Sales person).
I was offered the golden oportunity to swap my week (worth 4500 points) for that number of points upon payment of an Admin fee of only£1,699. ...or... I could have the 4500 points plus they would sell me another 3500 (to make 8000) for about £5.5K and if I did this the £1,699 admin fee was waived.
I declined both offers as both seemed to be rather expensiv, the resale week had cost us about £2.2K including fees and guaranteed us a two bed every year at a nice resort very close to school hols.
Within a week of returning home I received a letter from S-unterra Spain and the Balearics HO at Malaga. They offered 5000 points (an extra 500 as an incentive) if I converted to points at a cost of the normal admin fee of £299. I snapped their hand off. Clearly the sales team at GL were looking for a very much more expensive deal.
I do believe the timing of my fixed week purchase was very fortunate, at that time I believe GL was owned by CDM (or some similarly named firm) and S-unterra had taken on the Management of the Resort in exchange for access to all unsold inventory. My very good offer represented S-unterras method of buying up CDM inventory, I suspect GL is now managed and owned by DRI although I am not sure.
The offer you were made was decidedly ungenerous, if I were you I would approach the Company again and ask them what quantity of points they are prepared to offer for your week plus the standard admin fee of £299. They may not take this bait at all, but if they offered say even 3000 points then you could easily and cheaply take your points upto say 9000 for little more than £1,000 (see recent ad for disposal of 6000 points on this site).
It is probably a good idea to always decline an initial offer, when buying timeshare, weeks or points operators can usually do much better when asked the second or third time.