If you can score at least average on the CFA (see my sticky above for what constitutes average scores), I'd submit them now.
USNA will always consider your highest SAT/ACT scores. Thus, there is really no downside to waiting to submit them; if you get higher scores later, USNA will typically revisit your application, if that was the only thing standing in the way of an appointment.
In terms of your general question of a weak packet now vs. a strong packet later, it really depends on how weak, how strong, and how likely you can substantively improve it. The most important thing for USNA is your courseload in h.s. and your class rank. That's unlikely to change significantly first semester sr. year. Likewise, your sports and ECAs are mostly set (and you're allowed to project those activities in which you fully expect to participate sr. yr). Thus, there is little downside to waiting as it's unlikely you can do much to improve.
That said, if you think you'll fail your CFA or if your scores are very low (along with low grades and class rank), you may want to see if things improve first semester. But, by the time you have this info to submit, you'll be at the end of the line to have your packet reviewed.