Porch, a real estate technology venture and home improvement marketplace that has spent four years quietly renovating its own business, plans to become publicly traded through a merger that values the Seattle company at $523 million. The agreement, announced Friday morning, will combine Porch with PropTech Acquisition Corp., a special purpose acquisition company, or SPAC, as they’re known. The Los Angeles-based “blank check” company went public in November in a $172.5 million initial public offering with the intent of making such a deal.