5 of 5 added 24 characters in body

To some extent, what you see on Math.SE is under your control. For example, my experience improved when I added the following tags (among others) to ignored and checked "hide ignored tags" in preferences.

homework calculus linear-algebra algebra-precalculus 
sequences-and-series elementary-number-theory 
elementary-set-theory modular-arithmetic arithmetic 
soft-question trigonometry multivariable-calculus 
fractions big-list

This has effect on all views, including featured questions. There are 26 featured questions right now, but only 11 are visible to me (I also hide the tags in which I'm incompetent, which is a shamefully long list).

I obviously contributed to the increase of featured questions, being one of the site's top investors. But this growth is inevitable as the site itself grows. We passed 100,000 questions on January 24; now, less than a month later, we have 107,762. This is about 9,000 questions per month. Compared to this, having 30 or even 100 questions displayed more prominently for a week does not look wrong to me. As of now, StackOverflow has over 400 featured questions, and the additional exposure still works: questions do get more answers this way. The "featured" tab is just a convenient way for someone with limited time to find more difficult questions, as well as the questions that someone really cares about.

I had made a habit of receiving an answer in a few minutes [...] This is not happening any more.

This is a sign that you are asking deeper questions now than you did in the past. Congratulations! Some of your recent questions may have better luck at MathOverflow.

Update: My experience improved even more when I stopped ignoring tags and added the following CSS rules to my browser, matching them to *://math.stackexchange.com/*

.question-summary {
  display: none; 
.tagged-interesting {
  display: block !important; 
  background-color: #fff !important;

Which translates into: I see only questions with favorite tags, and since there is no need to highlight them now, their background is returned to white.