It depend yourself actually...see if you wnat to study...and have the interest to study or not.....
I don't mean getting a diploma is not good...it is better if you can get a diploma.....
However...I must tell you...there are many people who have only Nitec cert and do pretty well in their life...Graduate from ITE is not as "terrible" as one seem...you may not earn a lot of money la...but you won't "starve to death" lah....
Don't purse the diploma just for sake of getting the cert....if you get into poly study the course you not interest you..or not your future dream job...you also sianz right?
Somemore what if you fail your poly course how? retake the modules? then need money right? Imagine how much you going to spend when you are in poly...so I will advised you to study if you really have the heart to study....basically is don't waste your parent money la...spare a thought for them...if not go out to work also can....or study part time also can...
Of course getting a diploma is always better...but it is no guarantee...Actually I also worried to go poly...because my English really suck.....

...don't know can adapt to poly environment or not...