One of my best Creative Directors told me that design is about telling a story, I'd heard this statement before but never really seen it truly in practice. Countless tutors in school would say it but until I saw it first hand from being with that CD at the start of the project and then telling that story to the clients and explaining how we got from A to B it never really clicked.
So if design is a story, you should be able to tell that story no matter what you are designing - the way you got your teeth stuck in to the problem should scream through the project almost as if you were reading a good book and couldn't wait to turn that page.
I had a portfolio come across my desk recently from a designer telling me he wanted to specialise in houseware, so thats all that was in his portfolio minus one quick packaging project. Honestly I was bored, granted he didn't tell the story very well but still, I was reading the same thing no matter what project it was.
Whereas myself, even though I am now working in houseware and to get this job I had done a fair few houseware projects professionally I've also designed large office printers, tried my hand at designing a phone to test my abilities and it gives a bit of substance to my work. It also kept my now boss engaged and saw I had the ability to tackle something unfamiliar in a cohesive and thoughtful way.
So my advice would be to set your 'niche' at being a good designer, being able to understand what and who it is you are designing for and learn how to communicate the journey you took in an interesting way (the story).
Do that and it won't matter if you are designing trash cans or racing cars