I treated myself to some Proper Surround Sound kit over the long weekend, rather than relying on the tinny little speakers hidden inside the flatscreen TV. Relatively budget kit - £150 Yamaha receiver, and some £150 speaker/sub bundle - but...
The Man from Del Monte, he say Yes.
The difference is a revelation. I knew it'd sound a lot better but I didn't realise how much, or else I wouldn't have waited so long to do it. I think all my Blu-rays will be getting a re-watching!
A "Sound Bar" & Sub is almost essential I think. The bigger the LED screens get the worse their sound seems by comparison, very underwhelming.
Like you said, it doesn't need a huge amount of money to address it and Wireless Subs make it easy.
I think we paid £100 for a LG setup that can shake the house if required but also makes speech a lot clearer.
It also means we can us it as a HiFi by streaming music to the TV from a Smartphone (which seems like science-fiction now I type it).
Modern TVs are a bit like Sci-Fi now though aren't they?
The day we bought our big Sony my wife was showing me a photo on her phone and it came up on the TV behind her. No manual configuration took place, the TV just found her phone and decided it would become a 44" display for it (whether we wanted it to or not it seemed).