Your operative's particular skill improves as you level up. For example, the scientist collects +2 samples at level 1. For each level up, that increases by 1 so at level 2, the scientist collects +3 samples. Same goes for the rest of them for their respective skill which you can read for each operative on the Team screen.

I noticed the skill improvement for the security (resistance to damage), the scientist (sampling) and the medic (curing) and that was somewhat useful; on the other hand, the improvement of the diplomat's skill is not that helpful.
The initial 50% cut on the price of a new office is very nice, assuming the Diplomat can quickly reach an appropriate city (first time playing Ebola, I started in Buenos Aires and needed 3 turns to reach the epidemic zone, so in that case it was not that good)
However, by the time the diplomat got to level 2, I already have 3 or 4 offices up and running, so the extra cost reduction is less useful. I found that free offices for a diplomat at level 3 is totally useless, even more so with all the cash provided by 4 (or 5) active offices...
I would suggest to keep the initial advantage of a diplomat - the cost reduction on office building - but to provide a different advantage at level-up. By example, a 20% decrease in quarantine costs (15 k to 12 k).