I agree that the maintenace required by a diesel plant is low, but it is still much higher than that of solar. You will spent more man hours refilling the fuel than the total maintenance for the solar plant.
The rest of the post tries to compare apples to oranges. Either we compare technology currently available on the market. In that case the comparison I made is accurate.
Or you compared anticipated technolgies. In this case you have on the nuclear side proposals for inexpensive fuel cycles with greatly reduced risk. All of these designs will use more concrete per Watt electrical output so the energy paypack time will be greater than for current designs. But still these advanced reactors would be great improvements compared to current designs.
On the solar side there are concepts for designs that use much less material and less exotic materials. Thin film and metal based cells are on the verge of beeing market ready and there might be a breakthrough in polymere cells any time (so it is not guaranteed). By the time generation 4 reactors will be market ready solar power might be almost free.
Essentially it comes down to a bet that most of the industry currently is not willing to make: Gen 3 and Gen 4 reactors are designed to operate 65 years after a 15 year design time. Currently solar has a 20% to 30% cost improvement every year for 10 years now. Anybody putting his money on nuclear is betting that this progress suddenly stops before solar passes all other technologies. This might very well happen, but it might be smart to wait a few more years before commiting to an 80 year project competing with solar.