Curation rewards provides a financial incentive for users to spend a very significant amount of their time discovering good content.

NO, in terms of financial amount, the curation reward is far from enough to incentivise any users, including whales, to spend their time on the job.

When we talk financial, it's not the absolute amount that we should be looking, but the return-on-investment (ROI).

Just have a look at how much a Top curator can earns: http://steemwhales.com/trending/?p=1&d=1&s=cr
The average rewards received by the top-10 curators (my bot is among them) are somewhere 0.05~0.1% per-day, which translated into and ROI of 20~40% p.a.

While this figure might sound attractive to some guys, it's not attractive at all if you take into consideration the risk associating (There's high possibility that your SP will become valueless if Steemit couldn't turn out success).
And bear in mind that these return-rates can only be achieved with bots which mainly bring negative value to the platform. Most curators (including whales who running bots) are having an ROI lower than 15% p.a.

Those who honestly do manual curation will hardly get any better than 3%p.a.... and for the coming HF17 with more linear curve, we should see the rewards spread more evenly, which will result in overall lower ROI even for top curation-bots.

Any incentive that couldn't beat the minimum interest-rate or inflation in our real-world, is considered negative incentive.

IMO, the curation reward is never going to be a main reason that's drive people to do the curation.