For endgame, not so much...
For better or worse, Bioware has made the decision to give away most of the game's content. This leaves them in the position of trying to convince players to fork over cash for playing the game as a service. Thus, it does not appear that Bioware is keen for existing subscribers to switch to a non-subscription model and pay less. There are various things to unlock - including some extraordinarily petty options such as a charge to hide your helmet (certainly not mandatory, just petty) - but the bigger story is what you cannot unlock.
- Endgame content requires the purchase of consumable weekly passes per type of content you wish to play. Even at the most favorable exchange rate, unlocking two of the four types of content (raid, PVP, space combat, flashpoints) will cost you more than $15/month.
- Nonsubscribers are stuck with a currency cap that cannot be lifted. This limit applies not only to credits - the standard currency - but also the various token currencies used to purchase items.
- Nonsubscribers are also slapped with a permanent penalty to vendor prices, which includes gear vendors that take tokens.
- The cap plus the penalty combine to make it impossible for non-subscribers to purchase certain token rewards, and more generally require 25% more grinding at whatever you are grinding (raids, PVP, flashpoints, etc) for gear.
Leveling and grandfathered unlocks
Setting aside the endgame, what if, like myself, you are primarily interested in the game for the solo story content? This scenario is a bit more interesting.
There are certain restrictions that you can't lift (or won't want to pay for) including the currency penalties (you won't hit the credit cap but you may have problems with commendation vendors on planets) and restrictions on travel. There are also restrictions on your rate of exp gain, but that is ironically a mixed blessing in that I found the game's exp curve to be faster than I needed and skipped most of several planets to preserve challenge. And there are things you will probably need to pay for, such as access to your crewskills, probably a third hotbar (I don't know that all four that players had previously - or six that subscribers now get - are completely mandatory, but you will probably need a third bar).
Then there are an odd handful of things that can be unlocked in principle, but in practice are cheaper to unlock via a temporary subscription. Access to races - which are purely cosmetic in this game - will run you 600 Cartel Coins, but your existing characters are not affected when your subscription lapses. Your first two inventory upgrades can be paid for with 5000 and 20,000 credits as a subscriber, while non-subscribers must pony up 175 Cartel Coins per unlock - 350 total. In short, if you're looking to start up one - or better yet several - new characters, a one-month subscription may be the way to go.
And finally, there's the question of content. The new "Section X" content added with this patch will run non-subscribers 600 Cartel Coins. This content features new daily quests, which will be markedly less attractive to non-subscribers due to the currency issues, and the one-time questline for the HK-51 droid companion. This sort of content may well be more attractive as a rental than a permanent unlock.
On the horizon, Bioware plans at least one major content drop. It will also be interesting to see whether some of these restrictions get relaxed - either by default or through additional purchases - as the model matures. In the mean time, I don't regret my one-month subscription, and I might even see an advantage to subscribing for a month at a time periodically.
I suppose the risk you run - and perhaps the reason why Bioware is willing to make the temporary subscription attractive - is that you get used to the perks that cost money and do not want to give them up. Then again, I suppose that is a good thing to the extent that it would mean that you are playing the game and enjoying it enough to want to pay.