The key question to answer is this: Once the work is done, how much will my home be worth? This is called a "prospective valuation". The way it is done is to find other homes that have sold in your neighborhood that are similar in size and condition to what your home will become after having been remodelled.
A "remodel" usually brings the effective age of your home down. A 30 year old home could "effectively" be 5-10 years old if enough updating is done.
If a remodel will include adding square footage, it is important not to make the home a super-improvement for the area. If the typical home in your neighborhood has 2,000 square feet of livable area, I would not go beyond 2,500-2,700 square feet of additions. If you enlarge to 4,000 square feet, you'll never come close to getting your money back.