Hotel Apartments are presently the best form of long term investment that I have seen so far, although I dont think any HA properties have really started operation and it will be worth waiting to see how they go. Dubailand is a perfect choise for HA, and I am also looking for similar investments. If you find something let me know. By the way, the late 2007 prices in Dubailand stood at around 850 PSQFT, may have gone up by a minimum of 5% to a max to date of 15%
Im sorry i have no idea about Arjan as yet, but I will look it up. Quite frankly, the prices you have mentioned are on the higher side, but then it does depend upon may factors eg size, location, developers reutation, amenities, features, extras, freebies, etc.