While a antenna can help you will be hard pressed to gain 10 db or more on HF bands just with antenna. I have had many QSO's on 40 that would of been very difficult or impossible without a amp on both ends. I can generally work everything I can hear with a amp
There's a natural leapfrogging in the evolution of many stations. When I first started on 160M with 100W and no RX antenna, I could work everyone I could hear. Then I added a receive antenna... and all of a sudden there was a whole world of DX that I could hear but was a struggle to work. Then I added an amp... and now I can work everyone I can hear again. What that means: time to go to the next generation of receive antenna!
The local multi-multis are several generations ahead of me in terms of receive antenna technology on the low bands. And I thought I had a decent station on the low bands :-)
I've heard the term "alligator": all mouth and no ears. I'm more convinced than ever that if I can work everything I can hear... then I need a better RX antenna.