Its one of those things where if you are worried about your warranty then don't do it, although Nintendo still repair modded consoles if they become faulty.
In this case it is still a risk to whether Nintendo will do it or not, on over 85% of cases they have still repaired modded consoles for free.
Alternatively if you worry about the warranty and want it modded, just wait until your 12month manufacturer warranty runs out then mod it.
If you are not worried about the warranty then I would say if you really really want it modded then go for it.
Obviously you can play copied/downloaded games with a mod chip along with most imports but you don't have to use it for this reason as it is against the law although most people do use it for this reason.
A mod chip also lets you use Gamecube homebrew which is things like emulators, home made games, linux, etc.
Also with 1 of the mod chips you can fit an LCD screen to the Wii which displays the status of the Wii, you can also make the status light flash to the beat of music.
You can also watch videos from a disc and there is even software out now which lets you use real dvd discs in the Wii to watch movies.
There are both ups and downs about modding so it really depends on which way you look at it and what you actually want from your Wii.
It can go wrong, if you mess up the soldering during an install then you can mess your Wii at the same time. As long as it is fitted correctly you should have no problems.
A mod chip does not make the Wii completely region free either like a lot of people think, only some imports work but you have to be careful as some games have an update feature on them and if you update from most import games you can brick your Wii and end up with an expensive door stop.
If you only use games from your own region then no problems should happen.
I have a modded Wii myself and have had no problems since I modded it, the only problem I have is choosing which game I want to play because I have access to almost every Wii game released it does take away a lot of the fun as you can't decide on which game to play then when you do choose you play it for like 5 mins then want to play a different one.
For this reason I prob won't mod any future consoles I get unless I feel the need I really have to or there are features worth modding for added to the console due to modding.
You can play most games at least a few days before they are released from your own region and even a few months before they are released if you find the import one which works.
Like I said above, there are both ups and downs to modding, it all depends what you want out of your Wii.