This is very true, we can easily see in other countries that the female spouses can make the rather blah heirs shine (Netherlands, Denmark). I work for a Dutch company and those colleagues still make fun of WA being rather bland, not being the sharpest knife in the drawer, 'Prince Pils', but Maxima woaaaahhhh etc.
In Spain, this didnt work. Long before the gossip press went into overdrive about Letizia, from the day of the engagement, it seemed that people didnt really warm up to her, for whatever reason. It may be because of the way she comes across to many people, cold, bossy, not authentic (even the Prince said that she needs to smile more) and the way she was being handled by the royal house. Her work conduct may be flawless, but it hasn't been enough to win people over. Now the image that has been fed by the gossip press over the last 10 years sticks and it will be difficult to turn emotions around.
A royal man got married, has a few kids, grows some grey hair. Marriage and kids help to bring stability and maturity to a man. Of course some countries' pro monarchy press can praise their wives to bring that stability, but that just happened to every married royal man of this generation.
The last 10 years at least Letizia has made two big contributions to Felipe's royal career in a very difficult situation. Everyone in the Spanish press says these days Felipe's speech in Argentina, then the PoA awards, was a turning point of the public view, it was Letizia who had urged him to improve his pubic speaking since day one and had worked with him. The second thing Letizia had helped him to see more clearly Noos' business before the scandal broke. So Felipe was neither a complicit nor being seen leaving blind eyes as his parents (sure JC switched side when the scandal broke) or sister Elena. I doubt Felipe would be able to shine as today without the help of a woman with Letizia's background.