The Waldorf Blofeld is a great synth, both powerful and flexible. With careful programming you should be able to create sounds that are close to some of JMJ's sounds.
But for leads and basslines and effects I recommend getting a REAL analog synth as well as the Blofeld. Jarre nearly always uses real analog for leads, basses and effects. So to recreate this sound you should use something like a Tom Oberheim SEM Pro, Vermona Perforurmer/Mono Lancet, MFB Kraftzwerg, Doepfer Dark Energy, Analog Solutions Telemark/Leipzig/Vostok etc.
Effects processing (phasers, flangers, delays, reverbs etc) are also a big part of JMJ's sound.
So get the Blofeld for pads, strings and other polyphonic keyboard sounds and also get one of the analog synths I mentioned above for bass sounds and leads and effects. It would be a nice combination. Plus you will need a good quality effects processor (Lexicon MX300 or similar) and also get some analog effects pedals from Electro Harmonix.
Jarre's sound is a combination of different synths and equipment used together so I don't think you could recreate it with just one synth.
