I personally feel that the J-10B is critical to PLAAF's capabilities. J-10A gave China the imputes it needed to show the world that China has the means to defend itself against today's fighter-jets of the West. PLAAF has the J-10A in good numbers and is increasing it's fleet day by day. However, there comes a time in the evolution of an Air Power like PLAAF, where the employment of next generation capability is crucial to it's survival and hold on air supremacy on China's air space.
For this reason, the J-10B, with DSI, IRST, ECM, IFR, WS-10A, VL-RCS and produced in large numbers, would give China the ability to counter multi-dimensional threats.
No power, do date, has been able to match the U.S in producing advance fighters in large numbers. The Soviet Union, was only able to produce good enough fighters, who could challenge the U.S, if deployed on overwhelming numbers. That sort of approach really didn't work out for the Soviets. However, China being able to develop fighter-jets which have capability matching the U.S fighter-jets, is a real advantage. For that reason, China ought to produce sufficient number of J-10B's, J-20s, J-11B's and F-60's to be able to withstand and hit back any aggressor.
The development of the WS-10A engines and the engines for future Y-20 military cargo is essential to China attaining total independence in building, designing and developing military jets.