Gosh! It can really depend on your intentions - are you going to buy it and live there - and it's 50% below nearby sold comps? Are you planning to buy it and rent it out? It's really tough to even start to ask the right questions or provide advice without knowing more.
Naturally my instinct is to say, "walk away". I'd usually recommend buying a property at discount in a good neighborhood. Eventually you'll want to sell and have fewer objections by potential buyers.
L&I is the place to call, but this is likely only to generate a "clean and seal" - in which they will basically board up the property and post a notice on it. this can only be done if the homes are abandoned.
Homes that are lived in may well be current on taxes and simply kept in deplorable condition by the tenatns (not necessarily owners). Take into consideration whether or not you want such people for neightbors if the homes are occupied.
Often, I have found that many poorly kept properties are rented out and the tenants have illegal electric, gas or water connections. This will only impact you if they are tapping your electric, and/or if the illegal gas connection is leaking (you would probably smell gas but not be able to identify the location of the odor).
The city offices are overwhelmed and there are too few inspectors for the number of complaints and concerns generated. You will probably meet with the best response by directly contacting your Disctrict City Councilperson - their staff often can expedite issus like this. Good Luck!
The bigger picture I see as a realtor and as an investor is opportunity. I think buyers can negotiate a good deal for these properties that are next door to eyesores. The opportunity is in the future that chances are a new owner will purchase your next door property and rehab and do something great for the property. This type of turnover creates great neigborhood and can skyrocket certain neighborhoods. We live in Northern Liberties where over the years the people that purchased properties with shells on the blocks and abandoned properties have participated in one of the greatest appreciation areas in all of Philadelphia. There are still some shells available and when they sell, they will sell for more than many rowhomes in the rest of Philadelphia.
Hope that helps a little. I think it basically comes down to the block and location and the level of developement that is going on in the area. If you gave me more of the specific location, I could better answer the question.
Also, feel free to visit our website for more helpful hints ! Good luck !!!