Listen, there are some valid points about cross training. But for Pete's sake, most of it NEVER APPLIES TO MOST RUNNERS.
YES, if you're running "on the brink of injury", meaning, your mileage is so high than any increase in running will seriously risk injury, then YES by all mean supplement with cross training (if you're running 40mpw this does NOT apply to you).
YES, if you're getting older and you can no longer keep up the mileage and would like to cut back on your mileage and replace with cross training, then YES, cross training can help you and minimize the loss of fitness.
"Oh but you can get injured running 50mpw!" - YES, if you are stupid and running like an idiot with bad/wrong shoes, overweight or terrible form. If you are getting injured on low miles (under 70mpw), then you have bigger problems than cross training.
What the OP was asking, is whether cross training in and by itself can make you faster. The answer is NO. It is a decent substitute, but for almost everyone in the world who is running well UNDER their total potential training load, the best thing is to run more.
But let's face reality. MOST people attempt cross training because they are either too lazy or too scared of actually trying to push their mileage load even higher. Patiently increasing your mileage base to 100 mpw takes a lot of time, patience and effort. Most people would rather simply just hop on a bike / in a pool, actually have some "fun" with the variation and stay in their 60mpw comfort zone.
Comparing the above hobby joggers with people like Meb, who strategically cross trains because he is already over 100mpw, is a complete farce.