This problem is a good illustration of how we can create problems for ourselves by extracting information from records and leaving the context behind.
Scrolling back two images on the microfilm (New York Passenger Lists, 1820-1891, from NARA microcopy publication M237, Roll 46) to image 174 also gives you the name of the ship's master, Charles K Crocker.
Investigating Crocker's career, perhaps with an eye toward answering the question "How long was Crocker master of the Splendid?", would lead you to source material that also answers your question about the ship. If you are searching general textual material that has been scanned by OCR, you'll get more relevant hits searching for the surname "Crocker" or with the two items in combination than you'll get by searching for the name "Splendid" alone. Searching for Crocker and the Splendid together may help with the same-name problem; you are more likely to have the right ship named Splendid if Crocker is listed as her master.
You've made a good start by breaking down the task into specific research questions:
- When did the ship depart Liverpool?
- What type of vessel (sail powered or steam paddlewheel / prop) was the Splendid?
- What was the likely cost of passage?
- Who owned the ship?
- How long was the ship was in passenger service?
You may be able to answer all of these questions by searching in newspapers, both in general publication newspapers and in industry-specific publications such as Lloyd's List. Advertisements for tickets can give the cost of passage; schedules in advertisements and in shipping news can give you information that will help you estimate the time of passage. Since the questions are related (knowing the type of ship will give you an estimate of her speed), seeking the answers to any of the specific questions on your list is likely to lead you to information that will help you answer the others.
You've tried searching for the Splendid at the Immigrant Ships Transcribers' Guild but have you considered exploring the site for ideas about how to search and what you can search for? ITSG has sub-pages about newspapers and about sharing information found in postcards, journals, and diaries. Have you looked for manuscript collections?
Resouces for finding newspapers, online and off:
Resources for finding manuscript collections and other items in archives:
Topic Guides, articles, online exhibits:
To sum up: when a direct search for a person or a ship doesn't yield any results, widen your searches. Look for finding aids and research guides; look at websites, articles, and books with information about ships, and see what sources those authors have consulted. Keep a journal of your searches, and record not just where you searched, but how you searched -- what search terms you used, what keywords, what wildcards are allowed on each site. Record negative findings as well as positive ones. Write as you go and make a record, so you can go back and repeat searches later as your search skills improve.