I don't think the quality of anime has gotten worse in my honest opinion, there are still some really decent anime series out there - that are in the high school genre & there are plenty of interesting new anime series that are on their way out - off the top of my head in recent years; Kimi Ni Todoke, Tonari no Kaibutsu-kun, Beezlebub (which I found hilarious) etc etc etc there are some that are obviously mixes of other genres like To aru Majutsu No Index - I could name quite a few anime series that I'm a fan of that are of recent years & quite a few that are in the high school genre.
I do agree though that of late there seems to be an influx of anime that are centered around the high school genre - some aren't that great, some are decent, some are great, just like with any genre.
I partly get where your coming from - I can remember a whole lot more anime series being good that are pre 2008 - when we had series like Code Geass, Death Note, D.Gray-Man, Clannad, Toradora!, Rosario + Vampire, Kenichi the mightiest disciple, fullmetal alchemist brotherhood, full metal panic etc etc.
I think the biggest reason why anime is suffering is because the industry as a whole hasn't changed with the times - in the past - or the golden era, anime companies use to make their money primarily from rental shops (like blockbusters in the uk) & to a lesser extent a combination of licencing to national & international broadcasters depending on the shows popularity & in some instances on merchandise. But since the DVD market effectively collapsed along with the DVD rental market - so did the main source of revenue for production companies - the anime industry since then has been dropping off bit by bit & has never really recovered.
The issue with the anime industry is the same at the moment & the reason why quite a few anime production companies have been going defunct - it's mainly to do with the finance - many anime series require huge amounts of capital investment - I read somewhere the usual cost per episode is $150k-$300k. The problem solely lies with financial models - production houses have difficulty in making a return on the amount of capital they invest - it's as simple as that really.
So the longer the anime series the greater the amount of investment is needed & the greater the risk that they may not make any profit or even a return on their investment - this is why if you've noticed many anime series tend to only last 13 episodes whereas those that by chance do make a return, might get 26 episodes - the high-school genre imo is purposely chosen because most high-school genre based anime's don't have more than 13 episodes in story content - so it pretty much fits the bill ---------- most decent anime series need much more than 13 episodes - imagine if code geass, death note or the like had only been 13 episodes - any good anime series needs you to identify with the characters & like the story - that's hard to do when it's only 13 episodes - hence why you might feel the way you do.
There is much more to it than that obviously, but I don't really want to be sitting here for hours explaining it so:
http://www.animenewsnetwork.co.uk/feature/2012-03-05
If your really interested - the above link from
anime news network explains the crisis the anime industry is in at the moment - which is what I was briefly talking about - it also explains how production companies raise capital, avenues they use to make profit etc ect about the whole process & why the anime industry is in decline.
In short I think the anime industry salvation will probably be the internet but most production companies really haven't known how to make enough on the internet to at least cover costs & make some profit - at the moment what they are doing is making them more money but even that is barely much ---- advertising revenue is limited, anime DVDs are more expensive than usual DVDs so only not many are purchased, many watch anime for free on the internet - subscription seems the most logical choice but not everyone is willing to pay to watch anime they could watch for free & not everyone may be able to afford it.