When only looking at their keys...

The Jupiter 80 is definatley hot and worth bringing in, i think it has the best accoustuc sounds avaialable in hardware
Part of the V-synths technollogy found its way to the VP-770 too, but its not a really big seller.
I dont know if you still can back order the V-synth products, tough they are awesome.
The Gaia is a nice toy, but anyone that ever wanted to own one has it by now.
The Ax Shoulder keytar synths are unique and will sell, it will be a unique addition to your shop
The Fantom range probably is not for sale anymore.. so that leaves the GW8 as their only workstation, thats very subpar.
The Juno range of synths currently is not very popular.
Roland Pianos and auto accomp pianos sell very well, and are on par with Yamahas range on top of the market.
BK5 and BK7m offer a lot for their money
The E-line of arrangers is on the verge of becomming obsolete
The prelude is probably the best arranger a starting player can buy, but you will not be making a lot of money from it
The attellier and Combo organs are the best around by far..
The V-piano is still the best atage piano available..

So roland has a lot to offer... espescially if you will be selling Organs and pianos... Outside of that, Jupiter 80, the BK line and the Prelude might sell good, the other products are very situational..

I am expecting however a big new workstation any time soon, but no proof of that anywhere..

Roland however has grown huge in guitar effects market and such, and if you are also selling that stuff, sellling Roland is a no brainer, but if you are only selling portable keyboards... the BK7m, the Jupiter 80 and the keytar stuff will add something to your cutrrent range of keyproducts (If i am correct youre allready selling Yamaha, Korg and Ketron)

NEvertheless on the long run, Roland will allways remain a leading brand, and there will allways be Roland products in high demand.. if you dont have to invest in having them in stock, i would go for it...