Hey Truckinbear, if your current batteries work fine, why not just plan on keeping them for indefinite time, and just start like a side LiFePO4 fund where you put aside like $20 /mo (or whatever small amount you'd find insignificant to really notice), and then if you started to get to a point where the lead bank wasn't meeting your practical needs anymore, you'd have some decent deposit to drop on lithium (as it had been set aside for that)... Or is your current battery bank giving some kind of problem meeting your needs? If it's working fine, maybe just extract as much of its service life as you can...
There's nothing wrong with dinosaurs, hey you own it already, might as well get your money's worth... I know it's a lot, to 'want' to pluck down all that money at once for a new lithium battery system, but if you saved some side fund you just put aside gradually for this purpose well down the road, it might ease the pain later if you decided you needed to switch because of a real problem.
Unless of course you might be wanting to look into lithium so you can play around with it, like want to play with the technology or something... Or maybe it's for some other reason like tired of filling water, or dealing with gassing, ventilation, wasting more energy to charge and float them... Or whatever...
And, since lithium can range in price widely, for my lithium project, I did the cell level (build-your-own-battery) thing instead of turn-key battery, since it is much cheaper, and gives me visibility into own-BMS cell-level monitoring... I might go with a ready-made battery for a situation where I needed compact, portable, sealed, easy to move around battery, but for an indoor, home use battery bank, I would prefer to go with cells and build my own bank to get cheapest price, most kW/h for the buck...