Higher end is usually the first to get over built and weaken I find .. in many markets... 

No new builds or subdivisions, yet - to maybe weaken these older areas. 

That may weaken your offer, though. 

Also, any water drops left in the rubber gaskets or seals can weaken them and cause drips later.Wow, I didn't know it got that cold there!

Revealing other offers weakens my seller's position not only for the reason you outlined, but also because it lessens the chance to stoke a bidding war.

A HELOC is a debt position (and they count the entire available amount against you) that weakens your equity position on your primary.   

Without getting proper permits for plumbing, electrical, and weakening the loading structure you can get home redtagged resulting in buyer have to deal with the violation and have to pay cash for it.

I don't know if that would have been grandfathered, but it's dangerous so I change it for copper (short story: copper and aluminum expand/contact differently and over time their connections can weaken and result in a fire) The house I bought from 2001 was pure copper. 

I avoid buying projects that have major issues that potentially weaken or reduce your buyers pool.

The only downside I can see to a letter or personal appeal is appearing over-eager which could weaken your bargaining position.