Your hubs are a bit heavy and nowt so well sealed. Your rims are good (I run open pros and CBA upgrading as you need to spend a lot to make it worthwhile).
It’s worth investing in good wheels for a couple of reasons:
1. saving weight at the rim has a disproportionate effect on making the bike feel light (albeit losing weight doesn’t make you much faster).
2. a compromise in one area (hub or rim) can lead to a real PITA and is expensive to sort out.
Best value appears to be Planet X model B, as light as £300 wheels IIRC for £100 odd. But there may well be other areas where you might be better upgrading.
EDIT and I’d add if you go for new hubs or new wheels with open pros and better hubs you will not notice a difference when riding, it will only be a little static weight and more durability.
EDIT 2 if it’s for time trialling then aero rims are apparently faster but will be less comfy. No reason you can’t do the Ironman on your Ribble, just get it set up comfy, if you are taking it seriously then you will want an aero position.