So accurate punning aside.

The sanest advice you will hear on your problem is this Maemish...

Do a reflash.
Document everything if you do from the beginning....including your reflash...
So you have a bulletproof step by step of what happened where.
You go "off site" (as I like to call it...) and start experimenting ...then you have full documentation of what happens where.
The bad...and the good...
your unfavourable or favourable results can then be replicated .
your problems or successes can pin pointedly be scrutinized by those who can help ...and they SEE where the error or benefit originated.
Otherwise you are just "lucking out" with successes you have no idea how they occurred or how to replicate them...
or..
you are stuck in a mess ...likewise with no doc as to how exactly you got there...hoping someone says "Try this _____ ..." ....where they have no more clue than you as to what the hell results will occur from the trying...
THAT is Russian Roulette my friend.
And you are doing it with your n900 ...
which could end up in far worse shape than a simple reflash may ever fix.

Also...
sure install from devel and development ...
Know the risks of whatever you install and what conflicts there may be with other things already or you intend to install.
If there are no stated risks with what you are installing from devel / development cats. ...and you discover a conflict that creates issues on your n900...
you then have the documentation to show what interacts badly with what...
and you can post that as a certainty ...and a warning for others to avoid.
Then...reflash and follow your own docs to the point just before the problems began...
and continue with your experimentation.

And lastly ...
Don't go leaving devel and development enabled after installing something successfully ..
disable devel cats and re enable say ...reg cats ...again..
and don't utilize and install from different levels of cats at the same time...
normal extras ...testing extras and devel really need to keep their distance from each other ...
Don't enable any 2 or all 3 levels of cats at the same time and install stuff.
and playing with term and apt-getting or apt fixing is wielding a very big stick ...know exactly the effect of doing so are before just doing it...
and know what cats you have enabled at the time...

for example...JUST like any linux distro...when you install the system you choose during install which level of cats you want to pull from...regular stable cat , testing, or developmental / bleeding edge ...
But changing cats to install this or that from different levels ...will set you up for potential conflicts...
if you have stuff installed from various levels ...reg. testing and development ...on your device...and you properly enable say regular extras ...after installing from testing or devel cats ....and then you apt-get or apt fix or apt whatever...it is going to pull in what is needed from the regular extras , ...and most likely will conflict across the board with whatever you have installed that could conflict...from testing or devel. ... get it?
It will try to add packages for a prog that may or will have the same requirements for other progs for testing and devel progs ...but a different version...or your testing and devel progs may be required to purge ...purge and flush simultaneously others...and make a big mess you cannot unsnarl ..
You can do everything right Maemish... but because you are utilizing across possibly 3 catalogs ...using apt ...in any general format ...is going to have repercussions that are massive ..
If you wish to experiment....and use apt.
Stick to one level of cats...2 at the most.....and keep them close...like stable and testing...or testing and devel.. and never install from the others...if you intend on swinging a big apt stick...
It will limit the damage ...
but with even 2 different cat levels ...expect damage ...
It won't be as bad...as 3 levels of cat programs ...but you will still have damage..

In fact...
I am sure there are warnings about utilizing the different cat levels...
as well as warnings about how to use apt...
for the n900

For sure..
I for sure know that another individual just recently hit the install "all" button for 64 repos ..
enabling every possible conflicting cat , empty cat ...and dead cat along with it...
creating chaos for his cats.
This person was paying attention to only part of the instructions and not the whole...nor followed through with the warnings...
I pointed out what he needed to read ...

But I think for both of you ...
to quote Dr Strange...
"They really should put the warnings at the beginning of spells..."