I don't think a comparison between the early days of the cablecar and the DLR really makes much sense: the DLR came at a time of (and helped to further enhance) a time of enormous development - the construction of the Canary Wharf towers was not even underway when the DLR opened in 1987 (indeed, the original Canary Wharf station never opened: it was removed before the railway opened, to permit construction around the viaduct).
But more importantly: the DLR linked potential new workplaces with the rest of the London Transport network - it's easy to forget just how difficult to reach the Isle of Dogs was before the DLR: the Docklands Clipper bus (from Mile End) was a recent (mid-1980s, also funded by the London Docklands Development Corporation) innovation that penetrated the middle of the peninsula, along the newly constructed "red brick road". It's also easy to forget just how little there was on the Island in those years after the docks had closed.... the degree of development of housing, workplaces, and leisure facilities has been immense.
Of course this development had to take place for the DLR to increase its passenger ridership, which in turn demanded several rounds of capacity enhancement (extension of trains and platforms...), as well as all those extensions...
And the Beckton branch, in particular, took even longer to take off (and arguably still is not close to making the most of its potential). Arguably the Poplar-Stratford branch is less used than it might be, too - again related to the still incomplete redevelopment of some of the ex-industrial areas that surround some parts of the line.
Whereas; the cablecar....goes from nowhere to nowhere. Well, not quite, but pretty much. It doesn't provide new transport links, and it also doesn't have the capacity (or the scope for expansion) to undertake a great increase in ridership. It's a tourist attraction, pure and simple. And, because of its location, not a particularly convincing one (yes, it's fun to ride on, but still....)
The DLR was and is something else entirely - a vital part not just of the transport infrastructure, but a key element of the redevelopment of the wider Docklands area. No comparison.
(I remember that train crash, hanging off the viaduct - I think it was just before the railway opened to the public - and it was at the original Island Gardens station)