Well i shall give you my views that i have been experimenting with, however i have not performed it yet.
The way i look at the gimmicked and ungimmicked versions is this; they are completely different tricks, they are not 'more of a crush' and 'less of a crush'.
I think thats the problem people have been having with crush, they see the ungimmicked version as less powerful, when, in fact i think it is quite the opposite.
Two things i have found that improve the trick in just my eyes, (let alone the spectators) are firstly, how you decide to present it. Don't just say 'hey im going to crush this bottle', like Prae said before me, incorporate something to the effect of 'I have psychic powers - watch...'. Now i an understand that you may find this a bit too elaborate, but i came up with a neat little routine that i will happily share with you here, and anyone else who reads this.
You start by asking the spectators if they have seen the film "the men who stare at goats" (i recommend you see the film before using it as a reference in your performance), if they say no then explain that it is about a true story where the American army were trainign 'psychic spies', and how they used their minds to help them escape/fight etc. (If they say they have seen it, then skip the part i just mentioned.) Then describe one scene in particular, where George Clooney's character is sat staring at a goat, and it drops dead, after he has 'stopped its heart with his mind'. Explain that although you do not have the power to do that, you have been practicing manipulating things with just your mind, and say you will attempt to do so with a bottle of water (casually producing the bottle), empty the contents and tell them to watch closely, i found that it is more presentable if you place the bottle on the ground or a table, and move your hands in and out like Eric does on the DVD. Try and sync your hand movements with the crush, (it becomes easier after practice) and it becomes so unbelievable that people forget about anything that could cause the effect. (By the way, if you don't like pretending you have psychic powers, just say you will recreate the scene with the goat, but with a bottle instead.)
I thought that it adds a kind of relateability to the trick, as people know who george clooney is and even if they havent seen the film they might have seen the trailer, which has a clip from that scene on it. It helps them imagine the bottle as something completely different, and by the time it has seriously crushed, their minds are blown.
Thats my views on enhancing the performance, now for my views on enhancing the mechanics of the effect (i wont expose anything.)
Experiment with all the water bottles that you can find in your supermarkets or shops/vending machines etc, the most common ones. Experiment with timing and size and shape of the bottles and find a correlation that works suitably with the more common bottles (those of you who have the effect will understand me.) Green bottles or coloured bottles are usually more effective too (same again, you will know what i am referring to if you have it.
Once you have a good bottle, make sure you nail the factors that increase/decrease the crush until you can almost expect the same crush everytime. Then, if you want to perform it, just go buy the bottle you have experimented with, and go set it up (again, you will know what i am talking about if you have the trick, and where you should go to set it up), this way you can baffle even people you are hanging out with, because they saw you buy the bottle, and will have no idea how you managed it.
Hope all of that helps, it took me quite a while to come up with all of that when i was first experimenting with crush, but it allows for the ungimmicked method to be even more powerful than the gimmicked one, in my opinion.
Good luck!
EDIT: It is also very easy to get an incredibly powerful crush with the ungimmicked version, even more powerful than the gimmicked version because it is slower. Just spend time finding the right bottle and experimenting with timing and you shall achieve it perfectly every time.
