This tool, indeed, does that. 
(It doing that lets me feel slightly better about my $7k account valuation.)
Another interesting fringe case: Half-Life 2: Lost Coast is now only available via a $40 bundle, and is listed under that cost, but is actually just a pack-in bonus to the various Half-Life 2 bundles. How do I represent that? I originally had the $40 listing but updated it to "-" to reflect that the pricing isn't available.
Here's the summary I posted over on the Steam forums:
What it is:
Steam Gauge will let you get a summary of all the games/apps/etc listed for your Steam account via the Steam Web API. It returns information about those games including hard drive space requirements and cost (base store value, not what you actually paid).
-The list that is constructed allows you to individually select/de-select apps.
-There is a graphical representation of collection percentage selected vs total.
-There are pre-built options to select only a given app type (game, app, movie, etc).
-The app table allows you to sort the list by title, id number, hard drive space, type, and cost (just click the headers).
-If you don't have a vanity username set up, you can use your steamID64 number instead.
-If game information is missing from the database, it automatically adds that id to the list of apps to update in the next database refresh (simply using Steam Gauge helps make it better).
-Finally, you can export the results of Steam Gauge to a csv file, so you can manipulate the data however you wish.
-For now, your profile needs to be public.
-If you use a relatively modern browser, the whole experience is going to look/work better.
-The hard drive values are based primarily on the published requirements (where available) and is otherwise based on manual data checks of game install size.
-The database still isn't complete, especially for new games, and weird exceptions. It should still be helpful for general estimates, but the precision is limited to the data available.
-The mobile layout still needs a little work but should function properly.
-The "Value" column represents the base cost of the game, not what an account owner paid.
-Add more game information including genres, controller support and multi-player capabilities
-Add submission flag for games with missing/incorrect data to help crowdsource what I can't scrape
A while ago STEAM was rate limiting me to somewhere between 8-15 seconds (503's returned in between). Have you run into this at all on your end?
Edit: I was trying to datamine Steam several months ago as well, but the amount of data I needed really was unrealistic for this very reason, and it would have just been bad etiquette. I imagine by having this API they're having to deal with a ridiculous number of dataminers. And that's on top of their crazy number of normal users, which I'm sure the rate limiter is there to protect.
Steam gauge tells me the actual value of my games is $2019.05, but the amount I have spent is $432.75
I've actually collected a few other data points for each game as well, but I haven't figured out the best way to visualize / categorize them yet.
You might try it on your smartphone if you can - I still need to work on the mobile layout, but it shouldn't look terrible.
In any case, I looked at my list of games and play time on the Steam Client (on Mac) for the first time. It doesn't appear to be sorting correctly at all...for example, when sorting by "Playtime", the top listed game has "48.4 hrs on record" and then the next game is listed as "0.7"...and then the next game is "69.9" hours...It's kind of astounding to me how Steam is such a wonky, buggy platform given Valve's expertise.
Also, I really doubt that I've played Portal 2 for 70 hours. I guess it counts the time that I've left it minimized on the desktop. Though I admit, I am stuck on one of the latter puzzles and haven't gotten back to it...
(You'll notice "ClassyNemesis" is my profile name, but my account profile still links to http://steamcommunity.com/id/monkeyagent )
I have over $3k worth of games in my account, but I think I've actually spent maybe 15-20% of that, thanks to sales and bundles. I buy very very few games at full price these days.
Saw a couple of issues you could improve if you like:
1) Civilization 4 (and all DLC) shows up twice, but with no price
2) GTA3/VC/SA all show up twice
3) GTA1+2 show up as $50; you actually can't buy them on Steam, they're just in the $50 GTA Collection
4) Maybe remove 'the' when sorting
* When sorting by value it does a string comparison instead of comparing the numbers (4.99 > 19.99 where it should be the opposite).
Also, it seems like the value column is sorted like strings in Opera.
Pretty neat overall. I'm glad I bought most things at sale, and not the price shown..
Incredipede shows up as "Unavailable" in the list.
Here is the link to the steam page: http://store.steampowered.com/app/230150/
If they even did get the purchase date of the product, correlating that with every steam sale is probably nigh impossible.