Does this devalue my historic home?

The issue with RV’s is, if they are allowed, many people will have old junk sitting around & it devalues the neighborhood for others.

You are doing two things wrong, first you are devaluing your property by not charging market rents, value being based on income, and second you are risking legal action in the event of a injury.

There are many many things to play with but I was wondering if anyone has deliberately devalued their investment property before?

However, it is unlikely that these failures will result in a systemic devaluation of the market. 

If you want to keep track of the economic trends that impact local RE values, there's no better nor more pessimistic news outlet than Seattle Bubble, which is constantly scanning for signs of price devaluation and parses the factors down to the DNA level.

They perceive a threat  to quality of life, house values, and increased crime and devaluing a quality area.  

It's an interesting correlation he's looking at...he's basically devaluing homes in comparison to personal income data over the years. 

markets were flat through the middle 90s then started to roar back and by 97 made up the loss and by the peak of dot .com bubble made new highs.. then dot.com bubble hit and you have moderate negative impact on RE values only to come storming back and make new highs going into 08  GFC  but then the values dropped maybe 10% for prime BA RE.. not talking out in the Sac valley or other areas that got hammered with 50% devaluation because of extreme over building by the new home builders. 

Giving away money every month by supplementing your tenants rent from your pocket and devaluing your property  based on cap rates.A investor that does not realise their costs increase every year and therefor increase rents to maintain or increase profits should not be in business.