I think anyone on the fence should wait until after October 22, 2013. My reasoning is as follows:
1. Software updates do not always need to coincide with hardware updates. In fact, in the tech industry we see software revisions midway through major hardware revisions. This is a tactic to get products to appear newer or refreshed. But this is not a super solid point, I will agree.
2. Even though the ATV3 was updated in its hardware in January, it was not a major update but rather a cost saving update with certain components. Often times companies update their devices with newer, cheaper or cost effective components that have no impact on performance. This can also be seen in the video game industry with Playstation and Xbox console revisions. Components that change are usually as small as heatsinks and fans, and as big as chipset footprint sizes.
3. There is demand for new hardware. New devices arriving to the market like Chromecast are demonstrating features like streaming wherein they do not always stream from devices but also allow themselves to take over the stream so as to leave the devices free to use by the user. This and the need for more memory for apps to be offloaded to the ATV. Imagine running a game off your iPhone and have half the game load on the ATV's memory. This would allow for a more fluid and console like experience for gaming and would make sense with the incoming introduction of MFi game controllers in iOS 7. New specs are needed like Wifi 802.11ac, etc. which have been already explained in this forum.
4. Competition. The Chromecast is one thing, but now Roku is stepping up its game as well as Samsung with their SmartTV line. Apple needs to always stay on top, even if it means releasing a seemingly marginal update (iPhone 5S?). Also there are rumors of Amazon coming out with their own set top box. If Apple doesn't release an ATV4, then the average consumer will be holiday shopping for the latest Amazon box, which I am sure will make headlines as much as the Kindle Fire.
These are my opinions. Only time will tell. Again, if you're on the fence and $99 USD is a lot for you, then wait 1.5 weeks. You have nothing to loose. No one will point and laugh either because it'll be our little secret. 😉
TL;DR --> ATV4 will probably be announced on October 22 due to competition from Amazon & Google as well as needed support for powerful apps/games.