I would be hesitant to sign a 5 year lease. What if in year 2, something happens and you have to leave? Granted, you could find some other renters, but do you really want that hassle?
If they have not raised your rent in 4 years, it is likely the owners are older and the house is paid off. Thus, the rent is gravy, they like having reliable tenants, they already have enough money to live within their means, and don’t need to stir the pot by raising rent.
I have a similar situation, been in this pretty nice rental house, no rent raised in 10+ years. Landlady is old school, and elderly now. For the small stuff, I fix it and don’t bother her, considering I have a good rent. I have had the interior painted a couple of times, just because I like things looking nice and fresh. Replaced a 1970 large window AC, stuff like that. Figure that these improvements are a mere thanks to the landlady for not raking me over the coals all these years. She is similar to your owners, stock carpet, basic upgrades, etc.
Also, the less you have to bother with the owners, the better, they will be less inclined to raise rent, find new tenants, etc.
I would forgo any major improvements, and save your money, so when that gravy train ends, you have the means to buy a property of your own in Carlsbad.
