Splash Canyon was doing okay until the early 2000s, that's where the effects stopped being used and age started to set in on the animatronics. I remember the effects on Splash working and it looking okay as a kid, and I remember seeing it deteriorate over the years to what it was in 2017. When the designers had contracts with maintaining Pirate Adventure in the early/mid 90s, they'd spruce up Splash here and there too as a side job so it was definitely looked after in its early days.
Congo needs to have some treatment I agree. The concrete tunnel is more brutalist than Congo themed, if I am being honest. You could easily put something in there, be it tribal looking theming, water effects, more creative lighting, whatever. The actual layout could have more effects too. The problem you've got is that without seatbelts installed, a water effect is an invitation to stand up and with recent history of rapids accidents and the legal problems around it, it's not particularly wise. Oh and all pumps and waterfalls back on too...
Street ents should be there without question. It's the very least we should expect from a flagship UK theme park. After 2015, it made it all the more depressing when these were cut. Equally, it was great to see some return in recent years. But that's only scratching the surface of what Towers needs to be 'up to scratch'