Appraisals are available to other appraisals and they can, and do, affect home values within usually a six month time period. If a seller thinks that an appraisal is not accurate, the owner can request a review - usually done by yet another appraiser with more experience. If an owner wants an accurate appraisal, one that is done by a Lic. professional appraiser is the best way to go as he or she is paid for their services. If you are looking for a free market analysis, which may not be accurate, then use a professional real estate agent or broker. But, there will be an expectation that you will be listing with the agent or broker who has provided a service for "free." If you're thinking of selling in the near future, you may also consider hiring a professional home inspector. The Home Inspection report can help you identify things that "need" to be repaired along with items that "should" be repaired, and you'll get a better sense of items that "would be nice" to have repaired as well. Not only can you address the items that will be necessary for a buyer's bank to allow the sale, but, you'd have a head's up in terms of time and money needed for the repairs.
As for the specific question related to cost of a new garage door and "minor" upgrades to kitchen and bath, I think that a difference of only 12,500 is an absolute bargain when involving the two most expensive rooms of a house - kitchen and bath. If you can get these items done for much less, then you should do so because it will raise the value of your home. Otherwise, reducing the price by 12,500 for those repairs and upgrades is minimal. I've seen buyers offer much less due to just the stress of having to "deal with" repairs and/or upgrades. I've seen buyers who would rather spend upwards of $20,000 and more just to avoid painting one room. ...it's amazing how many people just won't lift a finger and would rather pay....So, if the appraiser has only reduced it by that much and has based the opinion on those repairs and upgrades, I think you should be grateful. You can either sell it to your brother and let him put in some sweat equity, or repair the property yourselves for a higher valuation. The bottom line here is this - there is a value for labor and the stress of repairs, and you should not discount or minimize the value of each.