Not unless you are planning on putting massive amount of systems and frequencies in your scanner and recording a lot, leaving the recordings on the SD card.
When I got my TRX I thought I'd need a larger card, too. I have several duplicate systems each with about 7000 RIDs and 3000 TGs in the list on at least 4 of the systems, another system with about 4000 RIDs and 500 TGs, I record some of the TGs and leave them on the SD card for a period of time, have 25 systems from across the state (some that seldomly get used but are there) along with about 2300 conventional channels. That said, I just checked the amount of space used and see I've only used about 244 mb of my 7.39 gb available.