It depends on your comfort with the material. Taking the INTRO gives you a good indication of your foundation for ICND. However, the INTRO exam is not as hard as the ICND based on feedback I've received. The ICND will also test INTRO concepts as part of the requisite knowledge to successfully answer questions. Many of the ICND and CCNA composite exam questions require you to apply several concepts to get a correct answer so there are more scenario-based questions to consider. If your INTRO foundation isn't strong, you'll have a hard time with ICND/CCNA.
For example, INTRO teaches the OSI and TCP/IP models so you can expect questions that require you to relate the two models or list the layers in order or map the layers between each model. ICND/CCNA assumes you know the models so may provide a diagram of devices (routers, switches, hubs, MLS) and have you identify segments, collision domains, and broadcast domains. To successfully answer the question you have to understand where each device fits in OSI or TCP/IP as well as the functionality each device adds to a network.
Just because you pass the INTRO doesn't mean you can forget everything you learned in Sems 1 and 2.