I've started my first business with £1,000 and bootstrapped my second tech startup up to proof of concept ahead of raising investment.

I agree with the advice you received; the amount of great business cases that come across investors desks these days will make it difficult for you idea to make it past the post box; but you never know. Sometime, it is simply a case of finding the right person at just the right time. The best thing you can do is take you idea as far as you can yourself and network like a ninja.

If you told us where you are in the world, we could possibly give you some additional practical advice.
For instance, I started my businesses in the UK and there are many other routes available to fund your startup and get a few accolades before approaching investors. Look at government backed startup loans and government grants.